In 1984, 12,790 Shigella isolates from humans were reported to
CDC. This is a 14.4% decrease from the 14,946 isolates reported in
1983. The number of isolates continues to be less than the 15,334
reported during the peak year, 1978 (Figure 2).
Shigella serotypes were reported for 12,179 of the 12,790
isolates. The most frequently isolated serotype, S. sonnei,
comprised
64.4% of all isolates serotyped (Table 3). S. flexneri 1a
accounted
for 14.1% of all S. flexneri subtyped; 1b, 2.6%; 2a, 28.1%; 3a,
24.3%;
and 6, 13.3%.
The number of reported isolates in every serotype decreased,
compared with the numbers reported in 1983 (Table 3). S. sonnei
decreased 15.3%; S. flexneri, 10.8%; S. boydii, 6.5%; and S.
dysenteriae, 3.2%. The decreases were not confined to one state or
region.
The age-specific rate of reported isolates per 100,000
population
was highest for 2-year- old children, lower for older children, and
lowest for adults. The age-specific rate for 20- to 29-year-olds
was
slightly higher than the rates for the older children and the
remaining age groups (Figure 3). In addition, in the 20- to
29-year-age group, a slightly higher rate was reported for females
than for males. Rates of reported isolates by patient sex were
similar for the remaining age groups.
Since some populations have higher rates than others, data were
tabulated separately for patients residing in certain institutions
(e.g. nursing homes, facilities for the mentally ill, and other
resident-care centers) and on American Indian reservations. Only
2,416 (18.9%) of the reports included data on residence at the time
of
onset of illness. Of those specified, 22 (0.9%) lived in
institutions, and 67 (2.8%), on Indian reservations. Fifteen
(68.2%)
of the reported isolates from residents of institutions were S.
sonnei, and five (22.7%) were S. flexneri. Twenty-four (36.4%) of
the
reported isolates from Indian reservation residents were S. sonnei,
and 42 (63.6%) were S. flexneri. For other known residences, S.
sonnei accounted for 1,634 (71.7%); S. flexneri, for 587 (25.8%);
S.
boydii, for 34 (1.5%); and S. dysenteriae, for 24 (1.1%).
Reported by Statistical Svcs Activity, Enteric Diseases Br, Div of
Bacterial Diseases, Center for Infectious Diseases, CDC.
Editorial Note
Editorial Note: This report is based on CDC's Shigella
Surveillance
Activity, a passive laboratory-based system that receives reports
from
the 50 states and the District of Columbia. These reports do not
distinguish between clinical or subclinical infections or between
chronic or convalescent carriers.
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