Outbreak investigation of Zika virus infection in seven districts of Saraburi Province, October 2023

Abstract

On September 29, 2023, the Joint Investigation Team (JIT) from the Office of Disease Prevention and Control Region 4,
Saraburi Province, was notified by the Situational Awareness Team (SAT) of a case involving an infant with microcephaly infected with the Zika virus in Kaeng Khoi District, Saraburi Province. The JIT, in collaboration with the Saraburi Provincial Public Health Office, the District Public Health Office, and, and Sub-district Health Promotion Hospitals, conducted an outbreak investigation between October 2 and 30, 2023. The objectives of the investigation were to confirm the diagnosis and outbreak of the disease, describe its distribution characteristics, identify the source of the infection and contributing factors, and propose prevention and control measures. The investigation followed a descriptive epidemiological approach, involving a review of medical records for infected patients, active case-finding for additional cases, laboratory testing, and entomological studies. The investigation identified 14 confirmed cases in 7 districts of Saraburi Province. These included 9 cases of microcephaly in infants and 5 cases in general patients. The general patients exhibited symptoms including fever (reported in all cases), rash (4 cases), muscle pain (2 cases), cough (2 cases), joint pain (1 case), headache (1 case), runny nose (1 case), and sore throat (1 case). The results of genetic material testing for the Zika virus using reverse transcription polymerase chain reaction (RT-PCR) from blood and urine samples from all 14 patients, conducted at the Bamrasnaradura Institute and Ramathibodi Hospital, detected the presence of the Zika virus in all cases. Entomological studies revealed that in the outbreak areas of Kaeng Khoi, Wihan Daeng, Nong Don, and Mueang Saraburi districts of Saraburi Province, the House Index (HI) exceeded 10% in all sub-districts. Aedes sp. larvae were found in household water containers such as cupboard legs, vases, and trays under refrigerators. The Zika virus outbreak in these areas was associated with both the detection of the Zika virus and a high density of Aedes mosquitoes. Risk factors contributing to the transmission and spread of the Zika virus included the timing of the outbreak during the rainy season and environments conducive to Aedes mosquito breeding, particularly in water-holding containers.