Influenza in Thailand: Status of surveillance and control, field performance of rapid testing, disease burden and cost

Background. Influenza is recognized as an important cause of illness, death, and economic losses in developed countries in temperate climates but little is known about influenza in developing tropical countries such as Thailand. Information is needed to guide national vaccine policy decisions.; Methods. The status of influenza surveillance, research, and vaccination in Thailand was reviewed. To describe the incidence and seasonality of influenza, between September 2003 and August 2004 all patients hospitalized with pneumonia and a sample of outpatients with influenza-like illness in a rural province was prospectively identified. Influenza infection was confirmed by cell culture, RT-PCR, serology, and a rapid influenza diagnostic test. Rapid test performance was compared to cell culture and RT-PCR. Medical record reviews, patient interviews, and national economic data were used to estimate losses due to influenza. Provincial data were extrapolated to construct national estimates of disease burden and cost.; Results. Vaccine distribution figures indicate that less than 1% of the population is immunized against influenza. The sensitivity and specificity of the rapid influenza test compared to viral culture was 77% and 96%, respectively. Influenza was identified in 80 (11%) of 761 pneumonia patients. The incidence of influenza pneumonia requiring hospitalization was between 18-111/100,000 population with a projected 12,575 and 75,801 hospitalizations nationwide. Children < 5 years of age and adults ≥ 60 experienced the heaviest burden. Influenza was confirmed in 252 of 1092 (23%) of ILI cases with peak activity in June-October resulting in a projected 924,478 outpatient visits nationwide. Influenza caused a projected U.S. {dollar}23.4 and {dollar}62.9 million in economic losses. The incidence of influenza was 1,420/100,000, a rate 43 fold greater than reported by the national passive surveillance system during the same period.; Conclusion. During 2003-04, influenza was a leading cause of severe pneumonia requiring hospitalization and an important cause of outpatient visits in Thailand. The seasonality of influenza suggests that March and April may be the most appropriate months to vaccinate. Economic losses attributable to influenza were substantial. Thailand's growing economy and effective immunization program may allow the country to consider targeted influenza vaccination to reduce the burden of disease.