Improving recognition of rickettsial infections in Sri Lanka: the value of combined qPCR and ELISA in acute febrile illness
File(s)
Accepted version
Author(s)
Type
Journal Article
Abstract
Introduction
In Sri Lanka, reliable diagnostics for rickettsial infections are limited. We assessed the burden, seroprevalence, and molecular diversity of rickettsial infections in hospitalized patients with acute undifferentiated febrile illness(AUFI).
Methods
AUFI patients were enrolled from the Western (n=540) and Central (n=260) Provinces. Clinical and exposure data, acute and convalescent sera, and buffy coat/eschar samples were collected. Orientia tsutsugamushi(OT) and Rickettsia spp. were detected using OT-specific (47 kDa) and pan-Rickettsia (17 kDa) qPCR assays. Group-specific IgG ELISAs were performed for scrub typhus(STG), typhus group(TG), and spotted fever group(SFG). Acute infection was defined by qPCR positivity and/or a ≥4-fold rise in IgG titres. Genetic diversity was assessed using OT 56kDa TSA and Rickettsia ompB gene sequencing.
Results
qPCR identified 38/800(5%) STG and 25/800(3%) TG/SFG infections. Among participants with paired sera (n=493), acute infections included 25(5%) STG, 11(2%) TG, and 17(3%) SFG cases. Overall, rickettsioses accounted for 86/800(11%) of AUFI cases. SFG seroprevalence was higher in the Central Province (17% vs 6%), while STG seroprevalence was higher in the Western Province (20% vs 13%). Genetic analysis on OT cases showed clustering with Karp, Kato, Buie, TH1811, TH1826 and Ikeda strains. Two cases of rickettsial infections were speciated as R. felis and R. sibirica. Only 19% of acute cases were clinically recognized and 58% received doxycycline.
Conclusion
Rickettsioses were under-recognized, highlighting the need for combining qPCR and ELISA diagnostics to strengthen clinical management and surveillance.
In Sri Lanka, reliable diagnostics for rickettsial infections are limited. We assessed the burden, seroprevalence, and molecular diversity of rickettsial infections in hospitalized patients with acute undifferentiated febrile illness(AUFI).
Methods
AUFI patients were enrolled from the Western (n=540) and Central (n=260) Provinces. Clinical and exposure data, acute and convalescent sera, and buffy coat/eschar samples were collected. Orientia tsutsugamushi(OT) and Rickettsia spp. were detected using OT-specific (47 kDa) and pan-Rickettsia (17 kDa) qPCR assays. Group-specific IgG ELISAs were performed for scrub typhus(STG), typhus group(TG), and spotted fever group(SFG). Acute infection was defined by qPCR positivity and/or a ≥4-fold rise in IgG titres. Genetic diversity was assessed using OT 56kDa TSA and Rickettsia ompB gene sequencing.
Results
qPCR identified 38/800(5%) STG and 25/800(3%) TG/SFG infections. Among participants with paired sera (n=493), acute infections included 25(5%) STG, 11(2%) TG, and 17(3%) SFG cases. Overall, rickettsioses accounted for 86/800(11%) of AUFI cases. SFG seroprevalence was higher in the Central Province (17% vs 6%), while STG seroprevalence was higher in the Western Province (20% vs 13%). Genetic analysis on OT cases showed clustering with Karp, Kato, Buie, TH1811, TH1826 and Ikeda strains. Two cases of rickettsial infections were speciated as R. felis and R. sibirica. Only 19% of acute cases were clinically recognized and 58% received doxycycline.
Conclusion
Rickettsioses were under-recognized, highlighting the need for combining qPCR and ELISA diagnostics to strengthen clinical management and surveillance.
Date Acceptance
2026-02-01
Citation
International Journal of Infectious Diseases
ISSN
1201-9712
Publisher
Elsevier
Journal / Book Title
International Journal of Infectious Diseases
Copyright Statement
Copyright © 2026 Copyright Owner. This is the author’s accepted manuscript made available under a CC-BY licence in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy)
License URL
Identifier
10.1016/j.ijid.2026.108460
Publication Status
Accepted
Article Number
108460
Date Publish Online
2026-02-04