In 1983, 14,946 Shigella isolates from humans were reported to
CDC. This is a 10.5% increase from the 13,523 isolates reported in
1982. The number of isolates is still less than the 15,334
reported
during the peak year, 1978 (Figure 1).
Shigella serotypes were reported for 14,089 of the 14,946
isolates. The most frequently isolated serotype, S. sonnei,
comprised
65.8% of all isolates serotyped (Table 1). When compared with
1982,
the number of reported isolates increased notably in all serotypes
except for S. flexneri, which remained relatively constant (Table
4).
S. flexneri 1a accounted for 13.5% of all S. flexneri subtyped; 1b,
13.2%; 2a, 25.4%; 3a, 18.5%; and 6, 11.3%.
The reported increases in the number of isolates from specific
serotypes were not confined to one state or region. However, from
1982 to 1983, reported S. sonnei isolates increased notably in
Indiana
(35 to 193), Maryland (85 to 199), Missouri (35 to 217), and New
York
(134 to 899). The increase in New York was associated with an
outbreak
in New York City.
The age-specific attack rate for persons from whom isolates
were
reported was highest for 2-year-old children, lower for older
children, and lowest for adults. The age-specific attack rate for
20-
to 29-year-olds was slightly higher than the attack rates for the
older children and the remaining age groups (Figure 2). In
addition,
in the 20- to 29-year age group, a slightly higher isolation rate
was
reported for females than for males. The isolation rates by sex
were
similar for the remaining age groups.
Since some populations have a higher attack rate 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 4,124 (27.6%) of the reports included data on residence at the
time of onset of illness. Of those specified, 49 (1.2%) lived in
institutions and 54 (1.3%) on Indian reservations. Forty-eight
(97.8%) of the reported isolates from residents of institutions
were
S. sonnei, and one (2.0%) was S. flexneri. Thirty-four (63.0%) of
the
reported isolates from Indian reservation residents were S. sonnei
and
20 (37%) were S. flexneri. For other known residences, S. sonnei
accounted for 2,918 (74.4%); S. flexneri 936 (23.9%); S. boydii for
39
(1.0%); and S. dysenteriae for 27 (0.7%).
Reported by Statistical Svcs Activity, Enteric Diseases Br, Div of
Bacterial Diseases, Center for Infectious Diseases, CDC.
Editoral 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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