International Notes Influenza Surveillance -- Wales, 1988-89

Important functions of influenza surveillance include early detection of epidemics--enabling immunization of persons not previously covered by routine immunization programs, notification of health providers to prepare for the possible impact on clinical workloads and hospital admissions, and characterization of prevalent strains to permit the timely production of appropriate vaccines. In 1986, a general-practice-based surveillance system was established in Wales to facilitate reporting of infectious diseases, including influenza and influenza-like illnesses. This report summarizes influenza surveillance findings in Wales for 1988 and 1989.

The surveillance system in Wales includes 34 practices with 138 doctors, representing greater than 240,000 patients (8% of the country's population). The age distribution of the practice population closely resembles that of the total Welsh population. Influenza-like illness (ILI) is defined as an illness that includes all the following manifestations: upper respiratory tract symptoms, fever, chills, myalgia, and cough. Each week, each practice reports the number of patients with ILI by age and sex to the Public Health Laboratory Service Communicable Disease Surveillance Centre, Welsh Unit; data are then summarized and disseminated in a weekly surveillance bulletin. Reports of increasing ILI prompt field sampling and assessment of laboratory isolations of influenza viruses.

During 1988 and 1989, the surveillance system detected an influenza B outbreak in March 1988, a predominantly influenza A(H1N1) outbreak in December 1988-January 1989, and an influenza A(H3N2) outbreak in November-December 1989.

Following the outbreak in December 1988-January 1989, the sensitivity of the reporting system was evaluated. A questionnaire was mailed to a random sample of 1344 patients aged less than 35 years in 10 reporting practices in South Wales; 878 (65%) persons responded. Of the 878 respondents, 240 (27%) reported an ILI that met the case definition during the outbreak period, and 103 of these reported that they had visited their doctor. Underreporting of physician contacts for ILI appeared to be substantial: based on actual reports, the cumulative rate for persons less than 35 years of age in these practices was 80 per 10,000; however, based on the survey findings, a rate of 1173 per 10,000 would have been expected if all patient contacts had been reported.

The outbreak in November-December 1989 was the first major influenza A(H3N2) activity identified since 1975-76; consequently, children less than 15 years of age were highly susceptible. During this outbreak, reports of ILI increased during the third week of October, and physicians were asked to submit throat swabs from suspected case-patients. The following week, the first influenza A virus isolation of the season (A(H3N2)) was reported from the North of England. In the second week of November, outbreaks of influenza were reported by four practices, and one influenza A virus isolate was obtained. The following week, 12 influenza A(H3N2) isolates were obtained from patients in one practice in West Glamorgan. By December 12, 1989, the four public health laboratories in Wales had isolated 23 influenza A strains from 144 nose or throat swabs and six strains from 73 nasopharyngeal aspirates. All isolates resembled the influenza A/England/427/88 subtype first detected in 1988-89 and were similar to the antigen contained in the vaccine used in 1989 (1).

In some practices, the number of visits and house calls for ILI was so high that the total number of cases could not be accurately recorded; thus, the data are probably an underestimation of the incidence of diagnoses made by general practitioners. Based on surveillance, the outbreak began in southwestern Wales and spread radially throughout Wales; the outbreak in West Glamorgan occurred 3 weeks before reporting increased in Gwent and North Wales. The cumulative age-specific incidence was highest in young children. By the reporting week ending December 20 (the week school terms ended in Wales), the rates had declined substantially in all areas. Reported by: SR Palmer, FFPHM, RL Salmon, MFPHM, RMM Smith, PhD, Public Health Laboratory Svc Communicable Disease Surveillance Centre, Welsh Unit, Cardiff Royal Infirmary, Cardiff, Wales. Div of Surveillance and Epidemiology, Epidemiology Program Office; Div of Viral and Rickettsial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The potential advantages of general-practice-based sentinel surveillance systems have been recognized in both Europe and the United States (2-4). This report on the experience in Wales illustrates how a surveillance system can provide early warning of influenza epidemics. In the United States, sentinel reporting from family physicians has complemented reporting from viral diagnostic laboratories, state and territorial health departments, and approximately 121 U.S. city vital records offices. The sentinel physician system provides information on the clinical impact of influenza and, because of the rapidity of reporting, provides the earliest indication of increased influenza in the United States.

Evaluation of the surveillance system in Wales included assessment of completeness of reporting and the relationship between reporting rates and population incidence. The evaluation findings suggested that only about 10% of patient contacts were reported by the general-practitioner-based system and that 43% of persons with ILI did not seek medical care. Although the reports provided an indication of the occurrence of an epidemic, they did not represent population incidence.

The November-December 1989 epidemic evolved over 7 weeks. Because of surveillance findings and notification, some health authorities had 2-3 weeks warning of the epidemic and sufficient time to implement appropriate public health measures (e.g., immunization of high-risk persons, antiviral prophylaxis, and increased staffing of patient-care facilities) to decrease the impact of the epidemic.

References

1. Public Health Laboratory Service Communicable Disease Surveillance Centre. Influenza surveillance in England and Wales, November 1989-May 1990. Communicable Disease Report, 90/22.

2. CDC. Surveillance of influenza-like diseases through a national computer network--France, 1984-1989. MMWR 1989;38:855-7.

3. Schaffner W, Scott HD, Rosenstein BJ, Byrne EB. Innovative communicable disease reporting. Health Services and Mental Health Administration Reports 1971;86:431-6.

4. Dodson DR. Sentinal active surveillance system. Missouri Epidemiologist 1989;(July):1-2.

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