Management of Scrub Typhus with Positive ELISA
Start doxycycline 100 mg orally twice daily immediately upon clinical suspicion of scrub typhus, without waiting for serologic confirmation, as early treatment markedly reduces mortality and morbidity. 1
Immediate Treatment Protocol
Initiate doxycycline 100 mg orally twice daily as first-line therapy for all patients with positive scrub typhus ELISA, regardless of disease severity. 2, 3
Continue treatment for 7-10 days minimum, with some authorities recommending up to 14 days to minimize relapse risk. 4
Expect fever clearance within 4-5 days of appropriate therapy; lack of clinical response within 24-48 hours should prompt consideration of alternative diagnoses or complications. 5
Critical Diagnostic Interpretation
A positive IgM ELISA is highly reliable for scrub typhus diagnosis, with sensitivity of 96-100% when compared to immunofluorescence assay (IFA), and specificity of 99%. 6, 7
The IgM capture ELISA using recombinant 56-kDa protein antigen is superior to the Weil-Felix test, which has poor sensitivity (67% in confirmed cases) and should not be used as the primary diagnostic method. 8, 7
Do not delay treatment waiting for confirmatory testing such as paired acute/convalescent sera or PCR, as clinical illness nearly always precedes laboratory diagnosis and early treatment prevents severe complications. 9, 1
Essential Clinical Assessment
Search meticulously for an eschar (black necrotic lesion at the site of chigger bite), which is pathognomonic for scrub typhus and may be found in unusual locations including the buttocks, eyelids, or other concealed areas. 2, 3
Examine for characteristic features: fever, headache, myalgia, and maculopapular rash appearing 4-6 days after fever onset. 10
Check for complications including intravascular hemolysis (dark urine, anemia), hepatitis, pneumonitis, meningoencephalitis, or acute kidney injury, which indicate severe disease requiring close monitoring. 2
Alternative Therapy
Azithromycin 500 mg daily for 7 days can be used as an alternative in patients with contraindications to doxycycline (pregnancy, documented allergy), though doxycycline remains the gold standard. 5
Chloramphenicol is FDA-approved for rickettsial infections including scrub typhus, but should be reserved for situations where doxycycline and azithromycin are contraindicated due to potential bone marrow toxicity. 4
Common Pitfalls to Avoid
Never rely on negative early serologic tests to rule out scrub typhus, as patients typically lack diagnostic antibody titers in the first 7 days of illness when most initially seek care. 9, 1
Do not use the Weil-Felix test as a confirmatory method despite its continued use in resource-limited settings; it has inadequate sensitivity (67%) and specificity for reliable diagnosis. 8, 7
Avoid withholding treatment in patients without visible eschar, as eschars are absent in many confirmed cases and their absence does not exclude the diagnosis. 10
Monitoring and Follow-Up
Reassess clinical response at 48-72 hours; persistent fever beyond 5 days suggests treatment failure, resistant organism, or alternative diagnosis. 5
Monitor for resolution of complications such as hemolysis, hepatitis, or renal dysfunction with appropriate laboratory testing. 2
No routine convalescent serology is required if the patient responds clinically to doxycycline and has a positive acute-phase ELISA, as this confirms the diagnosis. 6, 7