On 8 July 2021, a Zika virus (ZIKV) infection was laboratory-confirmed in a resident of Kerala state, south-west India. This represents the first Zika virus disease case ever reported from Kerala. ZIKV viral RNA was detected through RT-PCR testing at the National Institute of Virology (NIV) Pune, in a blood sample collected from the patient, a 24-year-old pregnant woman in her third trimester of pregnancy resident in Trivandrum district. On 28 June 2021, she was admitted to a private hospital with arbovirus like symptoms of fever, headache and general rash. Laboratory results were negative for dengue virus (DENV) and chikungunya virus (CHIKV). The woman delivered on 7 July, she was reportedly in good health and there were no apparent birth defects in the new-born. In the 3 months before delivery, she had resided in Trivandrum district not having traveled during that period. Among her close contacts, her mother reported having fever and similar symptoms one week before ZIKV confirmation in her daughter.
Retrospective testing was conducted among 19 hospital staff and patients at the same private hospital who had previously presented with fever, myalgia, arthralgia and petechial lesions in May 2021. Blood samples collected from these 19 ZIKV suspected cases were sent to NIV Pune, and on 10 July the laboratory results confirmed that 13 of the 19 samples tested positive for ZIKV by RT-PCR, indicating cryptic transmission of ZIKV in Kerala state since May 2021.
During the period from 8 to 26 July 2021, 590 blood samples were collected in Kerala state through active case finding and passive surveillance. Of them, 70 (11.9%) tested positive for ZIKV by RT-PCR at NIV Pune, including four additional pregnant women. All these cases were from Trivandrum district, except two cases reported from Ernakulam and Kottayam districts, who both had recent travel history to Trivandrum district.
On 31 July 2021, Maharashtra state also reported its first Zika laboratory-confirmed case from Belsar, a village of 3500 inhabitants located in Purandar Taluka administrative unit, Pune district. The case, a 50-year-old women, tested positive for both ZIKV (by RT-PCR and sero-neutralization) and CHIKV (by RT- PCR and IgM ELISA) at NIV Pune. Fifty-one additional samples from ZIKV suspected cases were collected from Belsar village, of them 40 tested negative for ZIKV and 11 are still pending for results.
So far, no cases of microcephaly and/or Guillain-Barre syndrome (GBS) have been linked with this outbreak.