BENEFITS AND LIMITATIONS OF THE WITWATERSRAND INFLUENZA AND ACUTE RESPIRATORY-INFECTIONS SURVEILLANCE PROGRAM

Objective: To establish an ongoing active surveillance programme for a cute respiratory infections in general, and influenza in particular. D esign: A network of 16 sentinel primary health care providers furnishe d morbidity information and clinical specimens for virus characterisat ion supplemented by school absenteeism and regional mortality data. Se tting: General practices, hospital outpatient departments and staff cl inics in the Witwatersrand area. Participants: Subjects treated for ac ute respiratory infections by 7 general practitioners, 1 specialist pu lmonologist, 4 paediatric outpatient departments, 1 mine hospital and university; factory and institutional staff clinics. Absenteeism data were obtained from 8 primary and 6 high schools in the region (represe nting 9 000 pupils). Outcome measures: Morbidity information and strai n characterisation of influenza isolates as well as other viral respir atory pathogens, school absenteeism, seasonal excess mortality. Result s: The most sensitive indicator of influenza activity was virus isolat ion, which gives an earlier warning signal of an impending epidemic th an morbidity or absenteeism parameters. Both morbidity and school abse nteeism provided quantitative indicators of the severity of the epidem ic. Mortality from all causes showed characteristic winter increases i n the 65-year-old and older population which were not seen in younger individuals. Circulating influenza viral strains matched the strains r ecommended for the vaccine in 1991 and 1992, but not in 1993. Conclusi ons: The course and extent of the annual winter influenza epidemic can be charted by means of an active surveillance programme, with sentine l primary health care providers furnishing morbidity data arid clinica l material from which virus isolations can be made. Antigenic characte risation of the isolates demonstrated that circulating strains may not match recommended strains in northern hemisphere-formulated vaccines and stresses the need for a southern hemisphere vaccine formulation fo r South Africa. Absenteeism information provides an indicator of the i mpact of influenza on the economy and excess mortality data emphasise the need for routine immunisation of the elderly.