Emergence of “urban scrub typhus” during Monsoon season in an urban pocket and biodiversity hotspot of New Delhi, India

Abstract

Introduction: Scrub typhus is an endemic disease transmitted within the “epidemiological tetrad” of rains, rodents, chigger mites, and scrub vegetation prevalent in “Tsutsugamushi Asia-Pacific triangle,” predisposing one billion population at risk and annual incidence of one million. Scrub typhus is difficult to differentiate clinically from coendemic vector-borne acute undifferentiated febrile illness (AUFI). Untreated scrub typhus may cause disseminated vasculitis, serositis, and hemophagocytic syndrome. Outbreaks of scrub typhus have been reported from Thailand, China, Korea, and rural India. Transmission of scrub typhus in urban areas is relatively rare. Three consequent outbreaks in a urban pocket in New Delhi, India, highlight emergence of urban scrub typhus. Materials and Methods: A cross-sectional, clinicoepidemiological, ambispective outcome surveillance study was conducted among all clinicodemographically homogenous patients presenting with AUFI during 2016–2018. Clinically suspected or intuitively investigated scrub typhus was screened by IgM/IgG immunochromatography and confirmed through IgM enzyme-linked immunosorbent assay and real-time polymerase chain reaction. Spatial, temporal, and vector surveillance through epidemiological mapping, line listing, and mite surveillance was done. Results: Scrub typhus outbreaks affected 161 patients during 2016–2018. Mean age was 31.77 ± 17 years. Most common clinical presentation was fever with headache. Eschar was present in 46.88% patients commonly on abdomen, chest, perineum, and extremities. Coinfections and comorbidities were seen in 3.75% and 14.37% patients, respectively. Seventy percent and 14.8% patients were managed in acute care and intensive care. Mean hospital stay was 8.96 ± 3.86 days. Doxycycline and doxycycline-azithromycin combination were given in 92.5% and 7.5% patients, respectively. All-cause mortality was 6.25%. 126/160 (78.75%) patients were geospatially distributed from urban landscape depicted in epidemiological maps. Temporal-seasonal distribution revealed bell-shaped curve from May to November. Mite carriage was seen in 16% rodents. Conclusion: Urban scrub typhus is emerging in microhabitats fulfilling the epidemiological tetrad and chigger mites undergoing transovarian transmission. Geospatial and temporal mapping are required in urban neighborhoods for risk stratification, outbreak management, vector control, and community education. A high index of suspicion in AUFI and early initiation of doxycycline therapy are required.