The burden of scrub typhus in India: A systematic review

Abstract

Background: Scrub typhus, a vector-borne zoonotic infection caused by the bacteria Orientia tsutsugamushi, is one of the most common and clinically important rickettsial infections worldwide. An estimated one million cases occur annually with a high case fatality rate. Although scrub typhus is a major public health threat in India, the burden and distribution remains unclear. We aimed to estimate the burden of scrub typhus in India.

Methodology: We performed a systematic review of published literature on scrub typhus from India to extract information on epidemiology, morbidity, and mortality. Important databases were searched using keywords and appropriate combinations. We identified observational, interventional, and population-based studies and extracted the data to evaluate the number of cases diagnosed using serology or PCR and the number of deaths due to scrub typhus. We conducted a systematic narrative synthesis to summarize included studies.

Principal findings: In the last decade, there were 18,781 confirmed scrub typhus cases reported in 138 hospital-based studies and two community-based studies. IgM ELISA was used in 122 studies to confirm the cases in majority (89%). The proportion of scrub typhus among acute undifferentiated febrile illness (AUFI) studies was 25.3%, and community seroprevalence was 34.2%. Ninety studies had data published on multiple organ involvement out of which 17.4% of cases had multiple organ dysfunction syndromes, 20.4% patients required ICU admission, and 19.1% needed ventilation. The overall case-fatality rate was 6.3%, and the mortality among those with multi-organ dysfunction syndrome was as high as 38.9%.

Conclusion/significance: Scrub typhus, a common acute febrile illness in India causing severe morbidity, accounts for a large number of deaths. The burden of the disease has been underappreciated. Early diagnosis and prompt treatment can significantly reduce complications and mortality. Establishing good surveillance and instituting appropriate control measures are urgently needed.

Fig 1. PRISMA Flowchart (Schematic representation of the study).

This figure describes the details of the data extraction process which describes and summarises the total number of articles identified from the search engines (PUBMED (N) - 1992, SCOPUS (N) - 567); total articles screened after filters applied and duplicates removed (N—1009); total number of full text articles assessed for eligibility (N—183) and the total number of articles included in the narrative synthesis (N—140).

Fig 2. Mapping the regional distribution of scrub typhus in India.

Number of scrub typhus cases less than or equal to 500 is represented as yellow, 501–1500 cases is represented as orange, 1501–2500 cases is represented as red and more than 2500 cases is represented as maroon. This map was created in the free version of ARC GIS by the first author. Please see the ARC GIS link https://arcg.is/1iDvKu. The base layer map was used from the Survey of India, Department of Science & Technology which gives open access to the general public https://indiamaps.gov.in/soiapp/.

Fig 3. Summary of significant findings relating to the Burden of Scrub typhus in India.

Scrub typhus is vector borne febrile illness in susceptible population caused by chigger bites harbouring Orientia tsutsugamushi. It was noted in this study that 81.7% of residents from rural areas exposed to shrubs are affected. Agricultural labourers (53.3%) were at the highest risks of contracting the illness. Community sero prevalence was reported to be 34.2% in India (*this was based on 2 community based study). 25.3% of all the hospitalised AUFI are reported to be scrub typhus. Among the severe scrub typhus cases 20.4% needed ICU admission and 19.1% were eventually put on ventilation. Multi organ dysfunction syndrome was reported in 17.4% of the patients. Scrub typhus has a case fatality rate of 6.3%. Further epidemiological studies need to be carried out to suffice the dearth of evidence of scrub typhus seroprevalence and severity in the community. The figure was created in Microsoft Paint and PowerPoint. The glass blades and mice silhouette are taken from https://openclipart.org/detail/164635/grass and https://www.publicdomainpictures.net/en/view-image.php?image=145546&picture=mouse-silhouette-sitting respectively and modified in Paint to get desirable effect.