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
Marier R. The reporting of communicable diseases. Am J
Epidemiol
1977;105: 587-90.
WHO. Weekly Epidemiological Record 1981;56:369-70.
WHO. Weekly Epidemiological Record 1981;56:377-8.
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