Driving factors of Zika virus outbreak in Urban areas, Nonthaburi, 25 July - 12 October 2016

Abstract

Background: On 3^rd September 2016, Nonthaburi Provincial Public Health Office notified the first two confirmed cases of Zika virus (ZIKV) in Bang Kruai and Mueang District, Nonthaburi Province. Bureau of Epidemiology, The Office of Prevention and Control 4 Saraburi and Surveillance and Rapid Response Team (SRRT) of Nonthaburi Provincial Public Health Office jointly conducted an investigation from 5th–25th September 2016.
Methods: A descriptive epidemiology study designed to describe the epidemiological characteristics, to confirm the outbreak and recommend surveillance and disease control measures. The population in this study was confirmed cases of ZIKV, household, workplace closed contact of confirm cases or people who were in Nonthaburi Province and had clinical presentation of Patient Under Investigation (PUI) following the Bureau of Epidemiology guideline. The active cases findings were conducted on 25 July to 12 October 2016. Urine and blood specimens were collected to confirm the infection of ZIKV by Polymerase chain reaction (PCR) methods. Shoe leather’ epidemiology by knocking on doors within 200 meters radius of all cases’ living and workplaces for controlling mosquitoes at the larval stage, survey of Aedes mosquito larvae at risk areas and collected mosquito to confirm ZIKV.
Results: We found 5 cases of ZIKV infection (3 confirmed cases and 2 household asymptomatic infection). The double cluster distributed in Bang Kruai and Mueang District, Nonthaburi Province. Clinical presentations of all confirmed cases were rash, fever and conjunctivitis. The onset date of cases were between 23rd August-11th September 2016. An active case finding showed 80 PUIs from 1,924 eligible medical records (22.58% of PUIs were followed up) and 61 PUIs and 192 pregnancy women from door-to-door survey. Laboratory results of all PUIs and pregnancy woman were negative for ZIKV. The larvae survey results on the first day showed House Index 71.43% (5/7), Container Index 20.00% (14/70) and day 5th showed House Index 22.15% (35/158) and Container Index 11.04% (65/589) respectively. Laboratory Testing for ZIKV Infection in mosquitoes found 2 Armigeres subalbatus (0.53% of 376 mosquitoes) positive.
Conclusions: This event confirmed outbreaks of ZIKV in 2 urban Districts, Nonthaburi Province. The percentage of larvae indices were not zero which could be the cause of the next outbreak and had found ZIKV in the Armigeres subalbatus mosquito which shown the virus circulation. Strengthening surveillance system is important to detect another PUI in the communities by raising awareness among local SRRT and catch one’s eye on pregnant woman in the affected areas.