Outbreak investigation of influenza A/H3 in the area of military camp, Nakhon Pathom, Thailand, July 2017

Abstract

On July 27th, 2017 09.00 a.m., Division of Communicable Disease Control, Nakhon Pathom Provincial Public Health Office was notified from Department of Social Medicine, Nakhon Pathom Hospital. The patients presented to the out-patient Department of Nakhon Pathom Hospital with suspected influenza infection. The primary information was found that there were approximately 10 draftees from some military camp in Nakhon Pathom Province. Patients presented with fever, cough and headache. The Surveillance and Rapid Respond Team (SRRT) verified and confirmed the data then contracted to the SRRT of Amphoe Mueang Nakorn Pathom for influenza control. Objectives: (1) To confirm the diagnosis and outbreak (2) To find the source and risk factor of outbreak (3) To describe the disease distribution (4) To control and prevent the outbreak. Descriptive and analytic case-control study were used as methodology for epidemiologic study. Results: The total cases were 73 cases accounting for 28.00% of the draftee or 9.97% of total camping soldiers. There was no hospital admitted case. The SRRT obtained the nasopharyngeal swab samples from 5 cases and confirmed the diagnosis of influenza by using real-time reverse transcriptase polymerase chain reaction (RT-PCR). The confirmed results demonstrated the genetic material of influenza A subtype H3. The first case presented his symptoms on July 23th, 2017, and then the most number of patients were found on July 26th, 2017. The first case went home in the north-eastern region of Thailand during 9-20 July, 2017 then he presented fever, headache and nasal congestion on July 23th, 2017. On investigation, the patient denied encountering with the previously infected persons. The results from analytic epidemiologic (retrospective cohort study) demonstrated that the most common risk factor was using glass together which was 2.70 times higher than that of people who did not use the glass together (RRadj = 2.70, 95% confidence interval 1.46-5.20, p<0.002). The trainer of soldiers and draftees were interviewed and revealed that 2 suspected outdoor activities were the risks of influenza outbreak. These activities may be the cause of this outbreak. Therefore, the SRRT analyzed the risk factor by using the epidemiological analyses and found that the outdoor activities (rid water hyacinth) is a risk factor for influenza infection. Relative risk of soldiers with outdoor activities was 2.03 times compared to the soldiers who did not join these activities (RRadj=2.03, 95% confidence interval 1.01-4.07, p<0.04). The interview revealed that this activity had risk of outbreak because the draftees drank water using the glass together. That drinking behavior may be the risk factor of outbreak influenza in the soldier camping. The SRRT of Nakhon Pathom provide support to prevent the spreading of this infectious disease by contacting Nakhon Pathom Hospital for providing oseltamivir to patients. The SRRT recommended the disease control measures to soldier in the camp that consisted of cleaning bedrooms and canteen, splitting spoon, glass and personal belongings, setting hands washing areas with water and soap, and screening the infected person. Moreover, the duration that the last patient was investigated for diseases surveillance was 2 times of the incubation period of influenza, until August 6th, 2017 that there was no new influenza case found afterward. Therefore, it was regarded as this outbreak ending.