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International Notes Expanded Program on Immunization: Using Survey Data to Supplement Disease Surveillance

The success of an immunization program in reducing morbidity and mortality from vaccine-preventable diseases can be measured only with a reliable disease surveillance system. Currently, the impact of WHO's Expanded Program on Immunization at regional and global levels is monitored primarily through national incidence figures, which are often inaccurate because they are based on incomplete data gathered in the routine surveillance systems. In many countries, more accurate incidence figures are needed to guide immunization priorities and targets.

Completeness of reporting depends primarily on two elements. First, the public must have access to health services and use them. Second, the health services must report cases accurately and regularly to appropriate public health authorities. The following examples show that loss of information within the health system is a problem in both developed and developing countries.

In one study in the United States, discharge records of 11 Washington, D.C. hospitals revealed that only 35% of selected notifiable communicable diseases were officially reported (1). In the Netherlands, the number of measles cases reported by sentinel stations was compared with the number reported by general practitioners. Only an estimated 3% of cases had been reported (2). In an Eastern Mediterranean country, 850 cases of tetanus were reported to the Ministry of Health. However, based on hospital chart reviews, the total number of patients with tetanus admitted to hospitals in the same period was 1,880. Thus, 45% were properly reported. In Thailand, based on polio prevalence surveys, routine reporting of poliomyelitis was estimated at 24%. However, wide variations in reporting were observed in different areas; 85% of the expected number was reported in the northern and northeastern areas. In a Western Pacific country, surveys showed that 85% of polio cases had been seen by medical practitioners during the acute phase of illness. However, comparison of the estimated annual incidence of polio, calculated from lameness surveys, with official polio incidence figures showed a reporting efficiency of only 12% (3).

To help overcome under-reporting, surveys have been conducted in many countries. In Tables 1 and 2, respectively, the results of 13 recent neonatal tetanus (TNN) surveys and 13 poliomyelitis surveys are compared with officially reported incidence figures to estimate reporting completeness.

Based on mortality rates in TNN surveys, an estimated 500,000 deaths from TNN occurred annually in the two regions (Table 1). Assuming that the case fatality rate for TNN is 85% and that TNN constitutes about 40% - 60% of all tetanus cases, approximately 1.2 million cases of tetanus occurred annually. The total number of all reported tetanus cases was 56,000. Thus, only approximately 2%-5% of all tetanus cases were detected and reported through the routine surveillance system.

Under-reporting of poliomyelitis in 13 countries from different regions was similarly estimated from lameness surveys (Table 2). Reporting completeness ranged from 1% to 26%.

The above examples indicate the magnitude of under-reporting using routine surveillance systems. In many countries, a great need exists to strengthen routine communicable disease surveillance. The task will be difficult, however, until there is easy access to health services and conscientious reporting. Until then, special surveys will remain periodically necessary to assess the completeness of existing reporting systems and to determine trends in actual disease incidence. Reported by WHO Weekly Epidemiologic Record 1982;57:361-2.

References

  1. Marier R. The reporting of communicable diseases. Am J Epidemiol 1977;105: 587-90.

  2. WHO. Weekly Epidemiological Record 1981;56:369-70.

  3. WHO. Weekly Epidemiological Record 1981;56:377-8.

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