Baffling Bacterial Infections

📋 Key Information Summary

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Tuberculosis — a great mimicker; consider TB in any chronic cough, weight loss, night sweats, or unexplained lymphadenopathy, particularly in migrants from high-prevalence countries, ATSI communities, and immunocompromised patients.
Latent TB infection (LTBI) is treated with 3 months isoniazid + rifampicin (3HR) or 4 months rifampicin (4R) to prevent reactivation; 9 months isoniazid (9H) remains an alternative.
Syphilis is resurgent in Australia, particularly among men who have sex with men (MSM) and in ATSI populations in remote northern and central regions; always test with treponemal + non-treponemal assays.
Primary syphilis presents as a painless chancre that may go unnoticed; secondary syphilis causes rash, condylomata lata, and mucous patches; neurosyphilis can occur at any stage and requires CSF examination + IV benzylpenicillin.
Infective endocarditis (IE) — suspect in persistent bacteraemia (especially Staphylococcus aureus, Streptococcus gallolyticus, HACEK organisms), new or changing murmur, and peripheral stigmata; use the modified Duke criteria for diagnosis.
Native-valve IE empiric therapy: vancomycin + gentamicin; prosthetic-valve IE: vancomycin + gentamicin + rifampicin; always obtain ≥3 sets of blood cultures before antibiotics.
Q fever (Coxiella burnetii) is the most common notifiable zoonosis in Australia; livestock workers are at highest risk; diagnosis requires paired serology (phase I and II IgG/IgM); doxycycline is first-line treatment.
Leptospirosis occurs in tropical northern Australia (especially cane workers, abattoir workers); can present as aseptic meningitis, Weil's disease, or pulmonary haemorrhage; treat with IV benzylpenicillin or doxycycline.
Brucellosis is rare in Australia but seen in returned travellers and in feral pig hunters (B. suis); treat with doxycycline + rifampicin for 6 weeks minimum.
All four infection groups require mandatory notification to state/territory health authorities under Australian legislation.
Aboriginal and Torres Strait Islander peoples bear a disproportionate burden of TB, syphilis, rheumatic heart disease–related IE, and certain zoonoses; culturally safe care and outreach are essential.
HIV testing is recommended for all patients diagnosed with syphilis, TB, or IE with risk factors; syphilis and HIV co-infection may accelerate disease progression and requires enhanced monitoring.

Introduction & Australian Epidemiology

Certain bacterial infections are notorious for their ability to masquerade as other conditions — presenting with vague constitutional symptoms, atypical physical signs, or misleading laboratory findings. In the Australian context, tuberculosis (TB), syphilis, infective endocarditis (IE), and the zoonoses Q fever, leptospirosis, and brucellosis represent a group of "baffling" infections that demand clinical vigilance, systematic diagnostic reasoning, and awareness of local epidemiology.

Each of these infections is notifiable under state and territory public health legislation, reflecting their significance for both individual patient management and population health. Australia's unique epidemiological landscape — including a large migrant population from TB-endemic regions, persistent sexually transmitted infection (STI) epidemics in ATSI communities, a significant livestock and agricultural industry, and tropical environments — creates distinctive risk profiles that differ substantially from other high-income countries.

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Diagnostic delay is the greatest risk. Misdiagnosis of TB, syphilis, or IE leads to prolonged morbidity, onward transmission, and preventable mortality. Always consider these infections in the differential of unexplained chronic illness, culture-negative endocarditis, and atypical presentations in at-risk populations.

Australian Burden of Disease

Infection	Annual Notifications (approx.)	Key Populations	Notification Status
Tuberculosis	~1,500–1,600 (2022–2023)	Overseas-born (86%), ATSI (~5%), people experiencing homelessness	Mandatory (all jurisdictions)
Syphilis (infectious)	~6,000–8,000+ (rising)	MSM, ATSI in remote communities, women of reproductive age (congenital syphilis rising)	Mandatory (all jurisdictions)
Infective Endocarditis	~3,000–4,000 hospitalisations/year	People who inject drugs (PWID), prosthetic valve holders, rheumatic heart disease (ATSI)	Not notifiable in most jurisdictions (varies)
Q fever	~500–700	Meat workers, livestock farmers, veterinarians	Mandatory (all jurisdictions)
Leptospirosis	~100–200	Cane farmers (QLD), abattoir workers, flood-exposed populations	Mandatory (all jurisdictions)
Brucellosis	~10–30 (rare, mainly zoonotic)	Feral pig hunters (QLD), returned travellers, unpasteurised dairy consumers	Mandatory (all jurisdictions)

Sources: Australian Government Department of Health, National Notifiable Diseases Surveillance System (NNDSS) 2023; AIHW; state TB registers.

🦠 Tuberculosis

Tuberculosis remains one of the most diagnostically challenging infections encountered in Australian practice. Its protean manifestations — from indolent lymphadenopathy to miliary disease, from asymptomatic radiographic lesions to fulminant meningitis — mean it must be considered in a remarkably broad differential diagnosis.

Classification

Type	Mechanism	Typical Presentation
Primary TB	Initial infection; often subclinical; Ghon focus ± regional lymphadenopathy	Children, recent migrants; hilar lymphadenopathy on CXR; may present with pleural effusion
Progressive primary TB	Failure to contain initial infection; direct progression to active disease	Immunocompromised (HIV, anti-TNF, corticosteroids); consolidation, cavitation, or miliary spread from the primary focus
Reactivation TB	Dormant bacilli reactivate (years to decades later), typically in the lung apices	Most common form in adults; upper lobe cavitary disease, chronic cough, haemoptysis, weight loss, night sweats
Extrapulmonary TB	Haematogenous dissemination to any organ	Lymph node (most common extrapulmonary site), pleural, skeletal, genitourinary, meningeal, miliary, pericardial, peritoneal

Clinical Features & Diagnostic Approach

Pulmonary TB: Chronic cough (≥2 weeks), haemoptysis, night sweats, weight loss, fever, fatigue. Upper lobe predominance on chest X-ray (CXR) with cavitation, infiltrates, nodules, or tree-in-bud pattern. Miliary TB shows diffuse 1–3 mm nodules.

Extrapulmonary TB — common sites:

Lymph node TB (scrofula): Painless, firm, matted cervical or supraclavicular lymphadenopathy; caseating granulomas on fine needle aspirate (FNA) or excision biopsy.
TB meningitis: Subacute meningitis with lymphocytic CSF predominance, low glucose, high protein; CSF adenosine deaminase (ADA) elevated; may be rapidly fatal if untreated.
Skeletal TB (Pott's disease): Vertebral body destruction, gibbus deformity; MRI is the imaging modality of choice.
Genitourinary TB: Sterile pyuria is the hallmark; renal involvement, epididymitis, or endometritis.
Pericardial TB: Constrictive pericarditis; pericardial effusion with elevated ADA; significant mortality if untreated.

Investigations

Essential Mycobacterial sputum (3 early-morning specimens) AFB smear (Ziehl-Neelsen), mycobacterial culture (BACTEC MGIT liquid + Löwenstein-Jensen solid), Xpert MTB/RIF Ultra (rapid PCR with rifampicin resistance detection). Turnaround: Xpert 2 hours; culture 2–8 weeks.

Essential Chest X-ray (PA + lateral) Upper lobe cavitation, infiltrates, hilar lymphadenopathy, miliary pattern, pleural effusion.

Available Interferon-gamma release assay (IGRA) — QuantiFERON-TB Gold Plus or T-SPOT.TB Supports LTBI diagnosis; cannot distinguish latent from active TB; not affected by BCG vaccination. MBS Item 69400 (IGRA). Available in all Australian labs.

Available Tuberculin skin test (Mantoux/Heaf) Intradermal 2 TU PPD RT23; read at 48–72 hours; ≥5 mm induration = positive in immunocompromised/household contacts; ≥10 mm = high-risk groups; ≥15 mm = general population. BCG may cause false positives.

Referral CT chest (high-resolution) When CXR is equivocal; tree-in-bud nodularity, centrilobular nodules, bronchiectasis, mediastinal lymphadenopathy.

Referral Tissue biopsy (lymph node, lung, bone, meninges) Caseating granulomas; AFB on histology; tissue PCR Xpert MTB/RIF; tissue culture is gold standard.

Available HIV serology All TB patients must be tested for HIV; dual infection common in migrants from sub-Saharan Africa, SE Asia.

Treatment — Active TB

All active TB in Australia should be managed in consultation with a TB specialist service (state/territory TB unit). Directly observed therapy (DOT) is recommended for all patients. Treatment is prolonged — minimum 6 months for drug-susceptible pulmonary TB.

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Never use a single anti-TB agent. Monotherapy rapidly selects for resistance. Always use combination regimens. Notify the state TB service immediately upon suspicion.

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Standard 6-month regimen (drug-susceptible pulmonary TB)

HRZE / HR · First-line combination

Intensive phase (2 months) Isoniazid 300 mg PO daily (5 mg/kg, max 300 mg) + Rifampicin 600 mg PO daily (10 mg/kg, max 600 mg) + Pyrazinamide 1,500 mg PO daily (25 mg/kg, max 2 g) + Ethambutol 800–1,200 mg PO daily (15 mg/kg)

Continuation phase (4 months) Isoniazid 300 mg PO daily + Rifampicin 600 mg PO daily

Adjunct Pyridoxine (vitamin B6) 25 mg PO daily with isoniazid to prevent peripheral neuropathy

Renal adjustment Ethambutol: reduce dose in eGFR <30; Isoniazid, Rifampicin: no adjustment required; Pyrazinamide: avoid if eGFR <10 (dialysis unit supervision required)

PBS status ✔ PBS General Benefit (all first-line agents)

Latent TB Infection (LTBI) Treatment

LTBI treatment is recommended for individuals at high risk of reactivation: recent contacts, IGRA/TST converters, immunosuppressed patients (anti-TNF, transplant, HIV, high-dose corticosteroids), and those with radiographic evidence of healed TB. Treatment decisions should be made with TB service input.

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3HR (preferred)

Isoniazid + Rifampicin · 3 months

Adult dose Isoniazid 300 mg PO daily + Rifampicin 600 mg PO daily × 3 months

Paediatric dose Isoniazid 10 mg/kg (max 300 mg) + Rifampicin 15 mg/kg (max 600 mg) daily × 3 months

PBS status ✔ PBS General Benefit

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4R (alternative)

Rifampicin · 4 months

Adult dose Rifampicin 600 mg PO daily × 4 months

PBS status ✔ PBS General Benefit

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Monitoring during TB treatment: Baseline FBC, LFTs, UEC, uric acid, visual acuity and colour vision (ethambutol). Repeat LFTs at 2 weeks, then monthly. Sputum culture monthly until conversion (2 consecutive negatives). Rifampicin is a potent CYP3A4 inducer — check for drug interactions (OCP, antiretrovirals, anticoagulants, immunosuppressants).

🔬 Syphilis

Syphilis, caused by the spirochaete Treponema pallidum, is experiencing a dramatic resurgence in Australia. Notifications of infectious syphilis have increased several-fold since 2010, with two distinct epidemics: one among MSM (predominantly urban) and one among young heterosexual ATSI people in remote communities (the ongoing outbreak declared in 2011 in northern and central Australia).

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Congenital syphilis is rising. Notifications of congenital syphilis in Australia have increased substantially since 2017. Every pregnant woman should be screened at first antenatal visit, with repeat testing in the third trimester and at delivery if high-risk. Untreated syphilis in pregnancy causes stillbirth, neonatal death, and severe congenital abnormalities.

Stages of Syphilis

Stage 1

Primary Syphilis

Painless chancre (ulcer with clean base, indurated edges) at inoculation site — genital, anal, oral. Appears 10–90 days post-exposure (average 21 days). Painless regional lymphadenopathy. Chancre heals spontaneously in 3–6 weeks even without treatment. Highly infectious.

Setting: Outpatient STI clinic / GP

Stage 2

Secondary Syphilis

Occurs weeks to months after the chancre. Generalised non-pruritic rash (including palms and soles — hallmark), condylomata lata (flat, moist perianal/genital lesions), mucous patches (oral), patchy alopecia, lymphadenopathy, hepatitis, meningitis, uveitis, nephritis. Constitutional symptoms: fever, malaise, arthralgia.

Setting: Outpatient / ED if systemic features

Late

Latent & Tertiary Syphilis

Early latent (<2 years): seroreactive, no symptoms; still potentially infectious via sexual transmission. Late latent (>2 years): seroreactive, not sexually infectious. Tertiary syphilis (rare in antibiotic era): cardiovascular (aortic aneurysm, aortic regurgitation), gummatous disease, neurosyphilis.

Setting: Specialist / tertiary care

Neurosyphilis — The Great Imitator

Neurosyphilis can occur at any stage of syphilis infection. It presents as: asymptomatic CSF abnormalities, acute syphilitic meningitis, meningovascular syphilis (stroke in a young person), general paresis (dementia, personality change), or tabes dorsalis (posterior column degeneration — ataxia, lightning pains, Argyll Robertson pupils). A CSF examination is required for diagnosis: VDRL in CSF is specific but insensitive (sensitivity ~50%); CSF pleocytosis (>5 WBC/μL) and elevated protein support the diagnosis.

Diagnosis — Serological Algorithm

Australia uses a reverse screening algorithm in many laboratories: initial treponemal immunoassay (EIA/CLIA) → if reactive, confirm with a different treponemal test + non-treponemal test (RPR or VDRL). Interpretation:

Treponemal EIA	RPR/VDRL	Second Treponemal Test	Interpretation
Reactive	Reactive	Reactive	Syphilis (current or previously treated) — treat if not previously treated or if RPR rising
Reactive	Non-reactive	Reactive	Possible treated syphilis, very early primary, or late latent — refer to specialist; repeat RPR in 2 weeks if early syphilis suspected
Reactive	Non-reactive	Non-reactive	False positive EIA — no treatment required

Treatment

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Benzathine Benzylpenicillin

Bicillin L-A® · First-line for all stages

Early syphilis (primary, secondary, early latent <2 years) Benzathine penicillin G 1.8 g (2.4 MU) IM × 1 dose

Late latent / latent of unknown duration Benzathine penicillin G 1.8 g (2.4 MU) IM weekly × 3 weeks (total 3 doses)

Neurosyphilis Aqueous crystalline penicillin G 3–4 g (18–24 MU) IV every 4 hours (or continuous infusion) × 10–14 days

Paediatric dose Benzathine penicillin G 50,000 IU/kg IM × 1 (early) or weekly × 3 (late) — same as adult schedules for children >30 kg

PBS status ✔ PBS General Benefit

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Doxycycline (penicillin allergy alternative)

Doxy® / Doryx® · Second-line (non-neurosyphilis)

Early syphilis Doxycycline 100 mg PO BD × 14 days

Late latent Doxycycline 100 mg PO BD × 28 days

Neurosyphilis Ceftriaxone 2 g IV daily × 10–14 days (preferred over doxycycline for neurosyphilis in penicillin-allergic patients; desensitisation is the gold standard if possible)

PBS status ✔ PBS General Benefit

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Jarisch-Herxheimer reaction: Acute febrile reaction occurring within 2–24 hours of initiating syphilis treatment (up to 40% of patients with early syphilis). Caused by massive spirochaetal lysis. Self-limiting (12–24 hours). Pre-warn patients. Treat with paracetamol 1 g PO PRN. Hospitalise if pregnant, neurosyphilis, or cardiovascular syphilis. Does NOT indicate treatment failure.

Syphilis–HIV Co-infection

All patients diagnosed with syphilis should be offered HIV testing (and vice versa). Co-infection is common, particularly among MSM. Key considerations:

HIV co-infection does not change the penicillin-based treatment regimen for syphilis.
Neurosyphilis may be more common and present atypical in HIV-positive individuals — have a low threshold for CSF examination.
Serological responses (RPR titre decline) may be delayed or blunted in HIV-positive patients — perform more frequent RPR monitoring (3-monthly rather than 6-monthly).
Syphilis enhances HIV transmission and acquisition; treating syphilis is therefore an HIV prevention strategy.
Check for drug interactions between syphilis treatment and antiretrovirals (rifampicin-based regimens interact with many ARVs — benzathine penicillin does not).

Monitoring & Follow-up

RPR/VDRL at 3, 6, and 12 months post-treatment (and at 24 months for late syphilis).
A fourfold (2-dilution) decrease in RPR titre = adequate serological response.
Treatment failure defined as: failure of RPR to decline 4-fold by 6 months, or a 4-fold rise in RPR after an initial decline. Investigate for neurosyphilis and retreat.
Partner notification is essential — trace contacts from the prior 3 months (primary) to 6 months (secondary) to 12 months (early latent).

❤️ Infective Endocarditis

Infective endocarditis (IE) involves infection of the endocardial surface of the heart, most commonly the heart valves. Despite advances in diagnosis and treatment, IE retains a mortality of 20–30%. It is a condition where delay in diagnosis is a major cause of preventable death, yet the presentation can be remarkably subtle — ranging from a subacute febrile illness to an acute, overwhelming sepsis syndrome.

Epidemiology & Risk Factors

Staphylococcus aureus is now the most common causative organism in Australia, surpassing viridans streptococci — reflecting the increasing role of healthcare-associated and PWID-related IE.
Native valve IE: Degenerative valve disease (elderly), rheumatic heart disease (ATSI populations), mitral valve prolapse with regurgitation, bicuspid aortic valve, congenital heart disease.
Prosthetic valve IE: Early (<1 year) — coagulase-negative staphylococci, S. aureus, gram-negative bacilli, fungi. Late (>1 year) — similar to native valve pathogens.
People who inject drugs (PWID): Right-sided (tricuspid valve) IE, overwhelmingly S. aureus (including MRSA). Increasingly common with methamphetamine and opioid use.
Indigenous Australians: Rheumatic heart disease remains a significant risk factor; Streptococcus gallolyticus (formerly S. bovis) IE mandates colonic investigation.

Modified Duke Criteria for Diagnosis

Category	Major Criteria
Blood culture positive	Typical organisms from ≥2 separate cultures: S. aureus, viridans streptococci, S. gallolyticus, HACEK group, Enterococcus spp. (if no primary focus); OR persistently positive cultures (≥2 positive cultures drawn >12 hours apart); OR single positive culture or Ixodes-associated Q fever
Evidence of endocardial involvement	Echocardiographic findings: oscillating intracardiac mass on valve or supporting structures (vegetation), abscess, new partial dehiscence of prosthetic valve, new valvular regurgitation

Definite IE: 2 major; OR 1 major + 3 minor; OR 5 minor criteria. Possible IE: 1 major + 1 minor; OR 3 minor criteria.

Minor criteria: Predisposing heart condition or IV drug use; fever ≥38°C; vascular phenomena (septic emboli, Janeway lesions, mycotic aneurysm, intracranial haemorrhage, conjunctival haemorrhage); immunological phenomena (Osler nodes, Roth spots, rheumatoid factor); microbiological evidence not meeting major criteria.

Investigations

Essential Blood cultures × 3 sets (aerobic + anaerobic) From 3 separate venepuncture sites, before antibiotics. Cultures positive in >90% of cases (if antibiotics not yet given). If prior antibiotics, take additional sets over 24–48 hours.

Essential Transthoracic echocardiography (TTE) First-line imaging; sensitivity ~70% for native valve, ~50% for prosthetic valve vegetations. Available in all hospitals.

Essential Transoesophageal echocardiography (TOE) Required if TTE negative or equivocal, prosthetic valve, S. aureus bacteraemia, or suspected complications (abscess, fistula). Sensitivity >90%. Perform within 24–48 hours of admission.

Available CT chest/abdomen/pelvis and cerebral MRI For embolic event assessment (silent emboli in ~30–40% of left-sided IE). PET/CT increasingly used for prosthetic valve IE diagnosis and monitoring.

Available FBC, CRP, ESR, UEC, LFTs, coagulation Inflammatory markers markedly elevated; normochromic normocytic anaemia; rheumatoid factor positive in ~50% of subacute IE (immunological minor criterion).

Empirical & Directed Treatment

All IE should be managed in consultation with infectious diseases, cardiology, and cardiac surgery teams. Prolonged IV antibiotic therapy (minimum 2–6 weeks depending on organism and valve type) is standard. Outpatient parenteral antimicrobial therapy (OPAT) may be considered for stable patients after initial inpatient stabilisation.

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Native Valve IE — Empirical (culture-negative or pending)

Vancomycin + Gentamicin · Empirical combination

Adult dose Vancomycin 15–20 mg/kg IV BD (target trough 15–20 mg/L) + Gentamicin 1 mg/kg IV TDS (adjusted to trough <1 mg/L for synergy)

Renal adjustment Both drugs require renal dose adjustment — consult pharmacy; gentamicin TDM mandatory

PBS status ✔ PBS General Benefit (hospital authority for vancomycin)

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Streptococcal IE (penicillin-susceptible, MIC ≤0.125 mg/L)

Benzylpenicillin ± Gentamicin · 4 weeks

Adult dose Benzylpenicillin 2.4 g (4 MU) IV 4-hourly × 4 weeks ± Gentamicin 1 mg/kg IV TDS × 2 weeks (first 2 weeks only, for synergy)

PBS status ✔ PBS General Benefit

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S. aureus Native Valve IE (MSSA)

Flucloxacillin ± Gentamicin · 4–6 weeks

Adult dose Flucloxacillin 2 g IV 4-hourly × 4–6 weeks ± Gentamicin 1 mg/kg IV TDS × 3–5 days (for rapid bactericidal activity in first days)

Renal adjustment No adjustment for flucloxacillin in mild–moderate impairment; gentamicin requires TDM

PBS status ✔ PBS General Benefit

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S. aureus IE (MRSA)

Vancomycin + Gentamicin + Rifampicin (prosthetic valve) · 6 weeks

Adult dose Vancomycin 15–20 mg/kg IV BD × 6 weeks (target trough 15–20 mg/L) + Gentamicin 1 mg/kg IV TDS × 2 weeks + Rifampicin 300–450 mg PO/IV BD × 6 weeks (add rifampicin for prosthetic valve only, start after initial bacteraemia cleared)

PBS status ✔ PBS General Benefit

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Surgical indications in IE (early surgical consultation recommended): Heart failure due to valve dysfunction; uncontrolled infection (abscess, fistula, enlarging vegetation); prosthetic valve IE with complications; large left-sided vegetations (>10 mm) with embolic events or high embolic risk; persistent bacteraemia >7 days despite appropriate antibiotics; fungal endocarditis. Refer to the 2023 ESC Guidelines for Endocarditis for full criteria.

Monitoring

Daily clinical assessment: temperature, heart failure signs, new embolic phenomena, neurological status.
Repeat blood cultures every 24–48 hours until culture-negative (document time to clearance).
CRP/ESR weekly — guide duration and assess treatment response.
Therapeutic drug monitoring: vancomycin (trough or AUC-guided dosing), gentamicin (trough and peak).
Repeat echocardiography: to assess vegetation size/response (TOE for prosthetic valve or complications).
Dental assessment: all patients should have a dental review during admission to address potential odontogenic source.

IE Prophylaxis — Australian Recommendations

Antibiotic prophylaxis for IE is no longer routine for most dental and minor surgical procedures. Australian guidelines (consistent with ESC/AHA) recommend prophylaxis only for the highest-risk patients undergoing the highest-risk procedures:

Patients: Prosthetic heart valve, previous IE, congenital heart disease (cyanotic or repaired with residual defects), rheumatic heart disease in ATSI populations (discuss on case-by-case basis).
Procedures: Dental procedures involving manipulation of gingival or periapical tissue, or perforation of oral mucosa.
Regimen: Amoxicillin 2 g PO 1 hour pre-procedure (adult); Amoxicillin 50 mg/kg PO 1 hour pre-procedure (paeds). For penicillin allergy: Clindamycin 600 mg PO (adult) or 20 mg/kg PO (paeds).

🐄 Zoonoses in Australia

Australia's large livestock industry, rural workforce, and diverse fauna create a unique zoonotic disease landscape. Q fever, leptospirosis, and brucellosis are the most clinically important bacterial zoonoses encountered in Australian practice. All three are notifiable diseases, and all three are notorious for being misdiagnosed due to non-specific presentations.

Q Fever (Coxiella burnetii)

Q fever is the most commonly reported zoonosis in Australia, with 500–700 notifications annually. C. burnetii is an obligate intracellular bacterium transmitted primarily by inhalation of contaminated aerosols from livestock (cattle, sheep, goats) — particularly during birthing, when extremely high concentrations are shed in birth products, faeces, urine, and milk. The organism is highly stable in the environment and can travel several kilometres on wind currents.

High-risk occupations: Meat processors, abattoir workers, livestock farmers, veterinarians, shearers, wool classers, laboratory workers.
Acute Q fever: Presents as undifferentiated febrile illness (fever, severe headache, myalgia, fatigue, hepatitis), pneumonia (focal or lobar), or hepatitis. Incubation 2–6 weeks. ~60% of infections are asymptomatic.
Chronic Q fever: Develops in ~1–5% of acute cases (higher risk with pre-existing valvular heart disease or vascular grafts). Most commonly Q fever endocarditis — culture-negative endocarditis; also vascular graft infection, osteomyelitis, hepatitis. Can present months to years after acute infection.
Post-Q fever fatigue syndrome: Occurs in 10–20% of acute cases; debilitating fatigue lasting months to years.

Diagnosis of Q Fever

Essential Paired serology (phase I and phase II IgG and IgM) Acute sample at presentation + convalescent sample at 2–4 weeks. A fourfold rise in phase II IgG is diagnostic of acute infection. Phase I IgG > phase II IgG suggests chronic Q fever. Available through state reference laboratories (e.g., QML Pathology, Sullivan Nicolaides, state public health labs).

Available PCR (blood, tissue) Useful in early acute infection before seroconversion, and for chronic Q fever. Available at reference laboratories.

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Doxycycline (acute Q fever)

Doxy® / Doryx® · First-line

Adult dose Doxycycline 100 mg PO BD × 14 days (start within first 3 days of illness for best effect)

Alternative Hydroxychloroquine 200 mg PO BD (used for chronic Q fever in combination; prolonged courses of 12–18+ months)

PBS status ✔ PBS General Benefit

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Hydroxychloroquine + Doxycycline (chronic Q fever / endocarditis)

Plaquenil® + Doxy® · Combination for ≥18 months

Adult dose Doxycycline 100 mg PO BD + Hydroxychloroquine 200 mg PO TDS for ≥18 months (minimum). Serial serological monitoring required — phase I IgG must decline to <1:200 before considering cessation.

PBS status ✔ PBS General Benefit

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Q fever vaccine (Q-Vax®): A licensed, effective whole-cell killed vaccine is available in Australia for high-risk workers. Pre-vaccination screening is mandatory (serology + skin test) to avoid severe reactions in previously sensitised individuals. One dose provides long-lasting immunity. Offer to all at-risk occupational groups. Funded under some state occupational health programmes.

Leptospirosis

Leptospirosis is caused by spirochaetes of the genus Leptospira. In Australia, the highest incidence is in tropical Queensland among cane sugar workers and those exposed to contaminated water or animal urine. Over 300 pathogenic serovars exist; L. interrogans serovar Hardjo and Pomona are the most common in Australia.

Transmission: Contact with urine or tissues of infected animals (rodents, cattle, pigs, dogs) via skin abrasions or mucous membranes; contaminated floodwater.
Incubation: 2–30 days (average 7–10 days).
Mild leptospirosis (anicteric): Biphasic illness — septicaemic phase (fever, headache, myalgia, conjunctival suffusion, meningism) → immune phase (aseptic meningitis, uveitis). Conjunctival suffusion (red eyes without exudate) is a characteristic but not pathognomonic sign.
Severe leptospirosis (Weil's disease): Jaundice, acute kidney injury, haemorrhage (pulmonary haemorrhage is the leading cause of death), myocarditis, DIC. Mortality 5–15%.

Diagnosis

Essential Leptospira serology (MAT — microscopic agglutination test) Gold standard; paired acute and convalescent sera; fourfold rise diagnostic. Available at state reference laboratories. Single high titre ≥1:400 in appropriate clinical context is supportive.

Available PCR (blood in first week, urine after first week) Available at reference labs; useful in early illness before seroconversion.

Available FBC, UEC, LFTs, coagulation, blood gases Leukocytosis, thrombocytopenia, elevated bilirubin and transaminases, AKI, raised CK.

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Mild leptospirosis

Doxycycline · Oral

Adult dose Doxycycline 100 mg PO BD × 7 days

PBS status ✔ PBS General Benefit

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Severe leptospirosis (Weil's disease)

Benzylpenicillin IV · Hospital

Adult dose Benzylpenicillin 1.2 g (2 MU) IV 6-hourly × 7 days. Alternative: Ceftriaxone 1 g IV daily. Start within first 4 days of illness for maximum benefit.

Paediatric dose Benzylpenicillin 50,000 IU/kg IV 6-hourly; or Ceftriaxone 50 mg/kg IV daily

PBS status ✔ PBS General Benefit

Brucellosis

Brucellosis is rare in Australia but should be considered in two settings: (1) returned travellers from endemic regions (Mediterranean, Middle East, Central/South America, Central Asia — B. melitensis, B. abortus); and (2) feral pig hunters in Queensland and northern NSW (B. suis), where infection is acquired through contact with infected feral pig blood during hunting and dressing. Australia is officially free of bovine brucellosis (B. abortus) and caprine brucellosis (B. melitensis).

Acute brucellosis: Undulant fever (wave-like fevers), drenching sweats, malaise, arthralgia, sacroiliitis, hepatosplenomegaly, lymphadenopathy.
Chronic brucellosis: Relapsing fevers, chronic fatigue, osteomyelitis (especially sacroiliac and vertebral), neurobrucellosis (meningitis, myelitis), endocarditis.

Diagnosis

Essential Brucella serology (Brucella agglutination test / Rose Bengal / SAT) Paired sera; fourfold rise diagnostic. Available at state reference labs. PCR increasingly available.

Essential Blood cultures (prolonged incubation) Notify the laboratory if brucellosis is suspected — Brucella requires extended incubation (up to 21 days) and poses a significant laboratory safety hazard (Risk Group 3).

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Standard brucellosis regimen

Doxycycline + Rifampicin · 6 weeks minimum

Adult dose Doxycycline 100 mg PO BD × 6 weeks + Rifampicin 600–900 mg PO daily × 6 weeks

Osteoarticular / neurobrucellosis Consider triple therapy: Doxycycline + Streptomycin/Gentamicin (first 2 weeks) + Rifampicin; or Doxycycline + Rifampicin for 3–6 months. Specialist ID input essential.

Paediatric dose Doxycycline (if ≥8 years) as above, or TMP-SMX 6/30 mg/kg PO BD + Rifampicin 15 mg/kg/day for 6 weeks

PBS status ✔ PBS General Benefit

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Laboratory safety: Brucella and Coxiella burnetii are Risk Group 3 organisms. Always notify the laboratory of suspected cases before specimen collection. Laboratory-acquired infections are well described and can be severe. Handle specimens under appropriate biosafety conditions.

Prevention of Zoonoses

Q fever: Q-Vax® vaccination for at-risk workers (mandatory screening pre-vaccination). Workplace infection control measures — P2 respirators, dedicated clothing, livestock management protocols.
Leptospirosis: Rodent control, protective footwear and clothing (waterproof boots, gloves), avoiding wading in potentially contaminated water, wound protection. No human vaccine available in Australia.
Brucellosis: Avoid contact with feral pig blood/tissues (wear gloves and eye protection during hunting), consume only pasteurised dairy products, cook pork thoroughly. Australia's national brucellosis eradication programme (BEF/Brucellosis-Tuberculosis Eradication Campaign — BTEC) successfully eradicated bovine brucellosis.

👥 Special Populations

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Pregnancy

Syphilis screening

Routine at first antenatal visit; repeat in third trimester and at delivery in high-risk women. Untreated syphilis causes stillbirth, neonatal death, congenital abnormalities (saddle nose, Hutchinson teeth, deafness, interstitial keratitis). Benzathine penicillin is the only effective treatment in pregnancy — doxycycline and ceftriaxone are contraindicated or insufficiently studied. Treat with Jarisch-Herxheimer reaction precautions and fetal monitoring.

TB in pregnancy

Standard regimen of isoniazid + rifampicin + ethambutol + pyridoxine is acceptable. Pyrazinamide: limited safety data in pregnancy, but WHO and many Australian TB services recommend inclusion (benefits outweigh theoretical risks). Streptomycin and fluoroquinolones are contraindicated.

Q fever, leptospirosis

Doxycycline is contraindicated in pregnancy (teratogenicity risk). For Q fever: trimethoprim-sulfamethoxazole may be used (avoid in first trimester and near term). For leptospirosis: benzylpenicillin IV is the preferred agent. Specialist ID and obstetric co-management required.

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Paediatrics

TB in children

More likely to present as primary TB (hilar lymphadenopathy, miliary, meningitis) than adult-type cavitary disease. Children <5 years at highest risk of progression to severe disease. All child contacts of TB cases require screening. Treatment: same agents with weight-based dosing; directly observed therapy strongly recommended. Pyridoxine supplementation essential.

Congenital syphilis

May be asymptomatic at birth or present with hepatosplenomegaly, rhinitis ("snuffles"), rash, osteochondritis, pseudoparalysis of Parrot. Late manifestations (>2 years): Hutchinson teeth, mulberry molars, interstitial keratitis, sensorineural deafness, saddle nose. Treat with IV aqueous penicillin G 50,000 IU/kg 8–12-hourly × 10 days (or benzathine penicillin 50,000 IU/kg IM × 1 if CSF normal and no clinical features).

Paediatric IE

Rare in children without congenital heart disease. Increasing incidence with central line use in NICU/PICU. Rheumatic heart disease is the primary risk factor in ATSI children. Same diagnostic principles as adults; modified Duke criteria apply.

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Elderly

TB

May present atypically — lower lobe disease, absence of cavitation, miliary TB. Pyrazinamide-associated hepatotoxicity is more common in elderly patients — closer LFT monitoring required. Consider rifampicin interactions with anticoagulants (warfarin, DOACs) and other medications.

IE

Degenerative valve disease is the primary risk factor. Enterococcus and S. gallolyticus are more common causes. Presentation may be subtle — "failure to thrive," confusion, or nonspecific deterioration. Higher surgical mortality. Gentamicin requires careful renal monitoring.

Syphilis

Tertiary syphilis (cardiovascular, neurological) may present in elderly patients with aortic aneurysm or dementia. Consider in the differential of unexplained aortic root dilation or rapidly progressive dementia.

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Renal Impairment

Drug dose adjustments

Ethambutol: reduce dose (or increase interval) in eGFR <30. Pyrazinamide: avoid if eGFR <10; consult TB service. Gentamicin and vancomycin: mandatory TDM; extended-interval dosing guided by pharmacy. Leptospirosis-associated AKI may require haemodialysis — drug doses must be adjusted to renal function.

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Hepatic Impairment

TB treatment

Isoniazid, rifampicin, and pyrazinamide are all hepatotoxic. Baseline LFTs mandatory. If ALT >3× ULN with symptoms or >5× ULN without symptoms: stop all agents, consult TB service. Reintroduce one at a time. Alcohol-related liver disease: higher risk of hepatotoxicity. Leptospirosis can cause severe hepatitis — monitor closely.

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Immunocompromised

HIV

TB: Higher risk of extrapulmonary and disseminated disease; IRIS risk when initiating ART (start ART within 2 weeks if CD4 <50, within 2–8 weeks if CD4 >50). Check rifampicin–ART interactions (use rifabutin if on protease inhibitors or certain NNRTIs). Syphilis: Atypical presentations, more frequent neurosyphilis, blunted serological responses; all patients with syphilis must be tested for HIV and vice versa.

Transplant / biologics / corticosteroids

Mandatory LTBI screening before starting biologics (anti-TNF, JAK inhibitors) or transplantation. IGRA preferred over TST. Treat LTBI before immunosuppression if possible. Q fever endocarditis risk is higher with immunosuppression — consider in culture-negative endocarditis work-up.

ATSI Health Considerations

Aboriginal and Torres Strait Islander Health

Aboriginal and Torres Strait Islander peoples are disproportionately affected by each of the infections discussed in this article. Addressing these disparities requires culturally safe healthcare, robust primary care engagement, and coordinated public health responses.

TB in ATSI Communities

While the majority of TB in Australia occurs in overseas-born individuals, ATSI Australians account for approximately 5% of notifications — a rate 5–8 times higher than non-Indigenous Australian-born individuals. TB in ATSI communities predominantly affects remote and very remote areas of the Northern Territory, northern Queensland, and Western Australia. Social determinants — overcrowded housing, delayed access to healthcare, and comorbidities (diabetes, smoking, chronic lung disease) — drive higher transmission and worse outcomes.

Syphilis — The Remote Outbreak

Since 2011, Australia has experienced an ongoing outbreak of infectious syphilis among young ATSI people (predominantly 15–29 years) across northern, central, and southern Australia. This outbreak has also seen a tragic rise in congenital syphilis cases. Contributing factors include limited access to sexual health services, stigma, workforce shortages, and population mobility. The Australian Government has funded enhanced STI testing, treatment, and contact tracing programmes through Aboriginal Community Controlled Health Organisations (ACCHOs) and state health services. Point-of-care testing (e.g., DPP Syphilis Screen & Confirm) is increasingly deployed in remote settings to enable same-day diagnosis and treatment.

Rheumatic Heart Disease & IE

ATSI Australians, particularly in remote NT, WA, and QLD communities, have among the highest rates of acute rheumatic fever (ARF) and rheumatic heart disease (RHD) in the world. RHD is a major risk factor for IE. The RHDAustralia programme (based in Darwin) provides clinical guidelines, register support, and education for ARF/RHD management. Any ATSI patient with RHD who develops new fever, embolic phenomena, or heart failure must be urgently assessed for IE.

Zoonotic Exposure

ATSI communities in remote areas may have significant exposure to zoonotic pathogens through hunting (particularly feral pigs — B. suis brucellosis), contact with livestock, and environmental exposure to contaminated waterways (leptospirosis). Culturally appropriate health promotion, protective equipment provision, and access to point-of-care diagnostics are important public health measures.

Remote access

Many remote communities lack access to specialist TB, ID, and cardiology services. Telehealth and visiting specialist clinics (e.g., Menzies School of Health Research outreach) are essential. OPAT programmes for IE or TB may not be feasible — prolonged urban transfers are sometimes required.

Housing & overcrowding

Overcrowded housing facilitates TB and respiratory pathogen transmission. Addressing housing is a health intervention. TB contact tracing in remote communities requires coordination with environmental health and housing programmes.

Cultural safety

Stigma surrounding STI diagnosis (syphilis), reluctance to discuss sexual health, and gendered healthcare preferences (preference for same-gender clinicians) must be respected. Use of Aboriginal health practitioners and liaison officers improves engagement. Yarning-based health education is preferred over didactic approaches.

Workforce

Chronic shortage of Aboriginal health workers, GPs, nurses, and specialists in remote communities. Locum and fly-in/fly-out services provide inconsistent care. Investing in local workforce development and ACCHO capacity is the most sustainable strategy.

Medication adherence

Long courses of TB treatment (6+ months) and IE treatment (4–6 weeks IV) are challenging with mobility, seasonal movement, and distance from services. Community-controlled DOT programmes, blister-packed medications, and mobile health unit support can improve adherence.

Notification & surveillance

Timely notification is critical for outbreak response. Point-of-care syphilis testing has improved notification rates, but under-detection remains a challenge. Close collaboration between ACCHOs, state health departments, and the Australian Government Department of Health is required.

📚 References

1. Australian Government Department of Health and Aged Care. National Notifiable Diseases Surveillance System (NNDSS) — Tuberculosis Notifications. Canberra: Commonwealth of Australia; 2023.
2. Denholm JT, McBryde ES, Eisen DP, et al. Management of latent tuberculosis infection in Australia: a position statement of the Thoracic Society of Australia and New Zealand and the Australasian Society for Infectious Diseases. Med J Aust. 2014;200(4):204–208.
3. Tiberi S, Muñoz-Torrico M, Duarte R, et al. New drugs and perspectives for new anti-tuberculosis regimens. Pulmonology. 2018;24(2):86–98.
4. Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine (ASHM). Syphilis: Australian STI Management Guidelines for Use in Primary Care. Sydney: ASHM; 2022 (updated 2024).
5. Australian Government Department of Health and Aged Care. Syphilis — National Notifiable Disease Surveillance System & Fifth National Aboriginal and Torres Strait Islander Blood-Borne Viruses and STI Strategy. Canberra; 2023.
6. Habib G, Lancellotti P, Antunes MJ, et al. 2015 ESC Guidelines for the management of infective endocarditis. Eur Heart J. 2015;36(44):3075–3128.
7. Delgado V, Ajmone Marsan N, de Waha S, et al. 2023 ESC Guidelines for the management of endocarditis. Eur Heart J. 2023;44(39):3948–4042.
8. Graves SR, Nguyen T. Q fever in Australia — current status and future directions. Aust Vet J. 2022;100(8):373–379.
9. Australian Government Department of Agriculture, Fisheries and Forestry. AQIS — Q Fever Management Plan and Q-Vax Vaccination Program. Canberra; 2021.
10. Slack A. Leptospirosis in Australia. Aust Fam Physician. 2010;39(2):67–70.
11. Robson JM, Harrison MW, Wood RN, et al. Brucellosis: re-emergence and changing epidemiology in Queensland. Med J Aust. 1993;159(3):153–158.
12. National Aboriginal Community Controlled Health Organisation (NACCHO). Sexual Health and Blood-Borne Viruses: Aboriginal and Torres Strait Islander Health. Canberra: NACCHO; 2023.
13. RHDAustralia (ARF/RHD writing group). 2020 Australian Guideline for Prevention, Diagnosis and Management of Acute Rheumatic Fever and Rheumatic Heart Disease. 3rd ed. Darwin: Menzies School of Health Research; 2020.
14. AIHW (Australian Institute of Health and Welfare). Aboriginal and Torres Strait Islander Health Performance Framework. Canberra: AIHW; 2023.
15. World Health Organization. WHO Consolidated Guidelines on Tuberculosis: Module 4 — Treatment: Drug-Resistant Tuberculosis Treatment. Geneva: WHO; 2022.