Monitoring Weil–Felix test in epidemic retinitis

PURPOSE: The objective was to study the positivity of the Weil–Felix test (WFT) in epidemic retinitis (ER) during the course of the disease. METHODS: This is a retrospective, observational case series of patients diagnosed with ER and presented to a tertiary eye care hospital in south India. Patients with positive WFT at the presentation, and who underwent a follow-up WFT during or after the resolution of ER were studied from September 2019 to March 2022. Patient’s demographics, timings of clinical presentation and resolution, and investigation details with a special focus on WFT positivity and its duration were noted. RESULTS: Sixteen patients were studied. Patients presented after 5 weeks of the fever (range: 2-12 weeks, median: 4). After 1-2 months, WFT was still positive in eight patients (50%). Only in one patient titers increased after 1 month, while in others, the titers decreased (n = 11) or remained the same (n = 4). Repeated tests in those patients (n = 6) after 3-4 months turned negative. Resolution of ER was seen at 1.35 months (range: 1-3 months) after the presentation. The mean duration for WFT to turn negative was 2 months from the presentation (range: 1-4 months) or 3.2 months of the fever (range: 1.5-6 months). CONCLUSION: In contrast to the reported physician’s observation of increasing titers of WFT after rickettsial fever, ophthalmologists may observe decreasing WFT titers in ER. The clinical resolution of ER may precede the normalization of WFT. Follow-up WFT titers should be studied in larger series in confirmed cases of rickettsial-ER to validate the affordable and readily available WFT in India.