Dengue, malaria, scrub typhus, leptospirosis, enteric fever and other rickettsioses in acute undifferentiated febrile illness in India: a scoping review

Background Acute undifferentiated febrile illness (AUFI) is a common clinical syndrome in India with overlapping features across infectious aetiologies. This scoping review mapped Indian studies reporting six predefined infectious aetiologies of AUFI (dengue, malaria, scrub typhus, leptospirosis, enteric fever and non-scrub rickettsioses) and described their geographic distribution and relative frequencies. Methods The scoping review was conducted using PubMed/MEDLINE, Embase, Scopus, Web of Science and the Cochrane Library from inception to 9 November 2024. Studies were included if they enrolled at least 100 AUFI patients in India and reported one or more of the six predefined pathogen groups with an extractable AUFI denominator. Study-level proportions were summarised descriptively. Studies were classified as broad-panel AUFI studies or pathogen-directed studies, and diagnostic methods were stratified by diagnostic certainty where appropriate. Results Ninety studies were included; 28 were broad-panel AUFI studies, and 62 were pathogen-directed studies. Dengue was reported in 63 studies, malaria in 30, scrub typhus in 27, leptospirosis in 28, enteric fever in 21 and non-scrub rickettsioses in 4. Among broad-panel AUFI studies, dengue was the leading selected aetiology in 13 of the 25 studies that tested for it; scrub typhus in 7 of 18; malaria in 4 of 24; leptospirosis in 3 of 21; and enteric fever in 1 of 21. Medians were higher in pathogen-directed than in broad-panel studies for malaria (32.1% vs. 8.6%), scrub typhus (20.0% vs. 12.5%) and leptospirosis (17.2% vs. 6.2%), but similar for dengue (25.3% vs. 27.5%). Most dengue studies used NS1 antigen or molecular testing (47/63), whereas most scrub typhus (20/27) and leptospirosis (23/28) studies relied on serology alone. Conclusion Published Indian studies of these six selected AUFI aetiologies show substantial heterogeneity across regions, study scopes and diagnostic methods. Broad-panel AUFI studies provide the more informative subset for descriptive comparisons across selected pathogens, whereas pathogen-directed studies are useful chiefly for mapping pathogen-specific evidence. The findings provide preliminary evidence to support the development and prospective evaluation of region-specific diagnostic approaches. They should not be interpreted as a complete assessment of all causes of AUFI in India.