Zika Virus Disease Outbreak Possibly due to Mosquito Breeding in an Abandoned Construction Site, Thiruvananthapuram, Kerala, India, May-August 2021

  • Vector-borne
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On July 8, 2021, Kerala, a southern state in India, reported its first-ever zika virus disease (ZVD) case in Thiruvananthapuram district. On July 9, blood samples of 13 staff of hospital-X (located in the city) collected during May 2021 as part of routine investigations for fever of unknown origin tested positive for ZVD. We investigated the outbreak to describe by time, place, person and institute preventive and control measures.

We defined a suspect case as the occurrence of fever or rash in any resident of Thiruvananthapuram from April 15, 2021, with at least one of the following symptoms - arthralgia, myalgia, conjunctivitis, headache, malaise, or a history of travel in the last two weeks to countries reporting zika transmission. We confirmed ZVD with a positive RT-PCR test of the blood sample. We conducted a door-to-door case search, established passive and entomological surveillance in the affected areas.

We tested 643 suspect cases and identified 66 (10%) confirmed cases [incidence: 20 per million] between July 8 and August 4. All case-patients were epidemiologically linked to the Thiruvananthapuram city, which reported the highest incidence (55/million). The incidence was higher among females (26/million) and in the age group 30-39 years (43/million) [Median (IQR) age: 33 (26-38) years]. We noticed a high Breteau Index (27.5%) in the Hospital X area and a high container index (20%) in an abandoned construction site behind the hospital. About 18% (6/34) of the Aedes mosquito pools were positive for zika virus.

The incidence of ZVD was predominant among females, younger age group (<40 years) and in urban areas. We hypothesised that Aedes mosquito breeding around hospital-X predominantly in the abandoned construction site could have caused this outbreak. We recommended strengthening vector control activities in the urban area and surveillance among females and younger age groups.

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