Standard operating protocol for Scrub typhus diagnosis and treatment

Abstract

Scrub typhus is increasingly recognised as a common cause of acute febrile illness in South and Southeast Asia. A lack of clinical suspicion and delayed diagnosis contribute to a mortality rate of ∼10%. A clinical diagnosis based on seasonal epidemiology, presence of eschar or rash, thrombocytopenia, hepatic or splenic involvement, and multiorgan dysfunction warrants prompt empirical treatment with doxycycline or azithromycin. IgM enzyme-linked immunosorbent assay remains the diagnostic mainstay. Treatment is stratified by severity; dual therapy is recommended in severe, confirmed cases. Most patients respond within 48 h of antibiotic initiation.

Keywords

Bacterial infection epidemiology diagnosis treatment

Diagnosis of Scrub typhus

A. Probable case/presumptive diagnosis

Clinical suspicion	Suggestive features (one or more)
Acute febrile illness Seasonality: Rainy/post-rainy months (oft June to November in India) Geography: Rural or semi-urban areas with exposure to vegetation, farming, or outdoor activity	Headache and/or myalgia Skin rash: Eschar (pathognomonic if present); maculopapular rash Hepatic/splenic involvement: Hepatomegaly, splenomegaly, or elevated transaminases Thrombocytopenia ± anaemia Interstitial pneumonia features: dry cough, dyspnoea, bibasilar rales, and/or radiological evidence Clinical syndrome compatible with any “SLUMED” infection (Scrub typhus, Leptospirosis, Undifferentiated viral fevers or sepsis, Malaria, Enteric fever, or Dengue)

Clinical suspicion

Suggestive features (one or more)

Acute febrile illness

Seasonality: Rainy/post-rainy months (oft June to November in India)

Geography: Rural or semi-urban areas with exposure to vegetation, farming, or outdoor activity

Headache and/or myalgia

Skin rash: Eschar (pathognomonic if present); maculopapular rash

Hepatic/splenic involvement: Hepatomegaly, splenomegaly, or elevated transaminases

Thrombocytopenia ± anaemia

Interstitial pneumonia features: dry cough, dyspnoea, bibasilar rales, and/or radiological evidence

Clinical syndrome compatible with any “SLUMED” infection (Scrub typhus, Leptospirosis, Undifferentiated viral fevers or sepsis, Malaria, Enteric fever, or Dengue)

B. Microbiological diagnosis

Test	Utility
IgM ELISA	Primary diagnostic test: high sensitivity and specificity
ICT	RDT used in emergency or peripheral settings. Sensitivity and specificity vary across commercial kits; generally lower than ELISA.
PCR (blood or eschar tissue)	Gold standard; limited availability. Sensitivity declines after the first week of antibiotic initiation. Yield is higher from eschar than blood.

Abbreviations: ELISA: enzyme-linked immunosorbent assay; RDT: rapid diagnostic test; ICT: immunochromatographic test; PCR: polymerase chain reaction.

C. Criteria for severe Scrub typhus in adults (any one)

System	Criteria
Respiration	ARDS: PaO₂/FiO₂ < 200 or SpO₂ < 92% with bilateral opacities on chest radiography
Cardiovascular	Hypotension, arrhythmias, or myocarditis (evidenced by cardiac enzymes or echocardiography)
Central nervous system	GCS ≤ 12, seizure, or meningitis/encephalitis (evidenced by CSF or MRI findings)
Renal	Creatinine ≥ 175 µmol/L (≥2 mg/dL) or acute rise > 45 µmol/L (>0.5 mg/dL) from baseline
Hepatic	Elevated transaminases with total bilirubin > 35 µmol/L (>2 mg/dL)
Coagulation	Platelet count ≤ 20 × 10⁹/L

N.B.: These six organ systems correspond to those assessed in the SOFA (sequential organ failure assessment) score.^1–4

Abbreviations: ARDS: acute respiratory distress syndrome; CSF: cerebrospinal fluid; GCS: Glasgow Coma Scale; MRI: magnetic resonance imaging; PaO₂/FiO₂: partial pressure of arterial oxygen to inspired oxygen fraction ratio; SpO₂: peripheral capillary oxygen saturation.

Footnotes

Author contributions

The author conceived the idea and drafted and revised the manuscript.

Declaration of conflicting interests

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Ashok Kumar Pannu

Flowchart Algorithm

N.B.: In pregnancy, azithromycin is preferred.

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