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Current Trends Human Salmonella Isolates -- United States, 1981

In 1981, 35,625 salmonellae isolations (including Salmonella typhi) from humans were reported to CDC. This represents an increase of 18.7% over the 30,004 isolates reported in 1980. The ten most frequently isolated serotypes comprised 68.7% of the total isolates (Table 1). Four of these accounted for 53% of the increase; S. typhimurium* alone accounted for over 30% (10,443 to 12,176) of the increase; S. enteritidis for 11% (1,904 to 2,554); S. newport for 8% (1,651 to 2,134); and S. muenchen for 4% (374 to 644). Increases were also reported in some of the less frequently isolated serotypes. For example, S. drypool increased 476% (17 to 98 isolations) from 1980; S. chester, 231% (55 to 182); S. hadar, 194% (47 to 138); and S. seftenberg, 138% (87 to 207).

The increase in isolates was not confined to one state or region. California, Georgia, Illinois, Louisiana, Massachusetts, Michigan, New York, and Ohio, accounted for 71% of the 18.7% increase. For some serotypes, increases were attributed to outbreaks in one or more states. Michigan and Ohio accounted for 44.8% of the increase in S. muenchen, part of which may be attributed to an outbreak associated with marijuana contaminated with S. muenchen (1). Seventy-nine percent of the increase in S. chester occurred in Massachusetts and Vermont; an outbreak associated with this serotype was traced to roast beef in Vermont (2). A 39% increase in S. newport occurred in New Jersey, Pennsylvania, and Washington; increases were associated with eating pre-cooked roast beef in New Jersey and Pennsylvania (3). An outbreak of S. newport was reported in Washington, but no vehicle was identified. Eighty-seven percent of the increase in S. drypool occurred in California, Ohio, and Texas; outbreaks were reported in Ohio and Texas (4). Illinois, which accounted for 90% of the increase in S. seftenberg, reported an outbreak of this serotype in a prison system. Increases in S. hadar, S. typhimurium, and S. enteritidis were not confined to any single state. *Includes S. typhimurium var. copenhagen

Figure 1 shows the reported age distribution of persons from whom isolates were obtained. The rate was highest for 2- to 4-month old infants, decreased abruptly among age groups of early childhood, and then remained constant through the adult years. The rate of Salmonella isolation was slightly higher among males than among females in the 20-year age groups; it was slightly higher among females than among males in the 20-69 year age groups. This is consistent with data from previous years. The increase in reported isolates occurred in all age groups; however, the largest increases occurred in the 20-29, 30-39, and 40-49-year age groups. During the past 14 years, the median age of all persons from whom isolates were obtained has continued to increase, from a median of 6 years in 1968 to 12 years in 1981. Table 1 reports the median age of persons from whom isolates were obtained for the 10 serotypes of Salmonella most frequently isolated.

In 1981, 38 of 604 reported isolates of S. typhi were from carriers, 195 from cases, and the remaining 371, undesignated. The carriers' median age was 61.0, while that of the new cases was 23.0. 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 the Salmonella Surveillance Activity conducted by the Association of State and Territorial Epidemiologists and by CDC. It is a passive laboratory-based system that receives weekly reports from the 50 states and the District of Columbia and regular summaries from the U.S. Department of Agriculture. The reports do not distinguish between clinical and subclinical infections or between chronic and convalescent carriers. Many selective factors affect whether an infection will be reported. Despite such restrictions, these data provide a basis for comparison with past and future tabulations.

The number of reported Salmonella isolations has been steadily increasing since 1977, but the 1981 annual increase of 18.7% is larger than in previous years. Some of this may be artifactual, but increases seen annually are probably not all the result of artifacts. The disproportionately greater increase among young adults in certain states suggests possible recent increases in exposure of this age group to specific contaminated vehicles in certain areas of the country. The gradual increase in the median age of all cases of salmonellosis in the last few years may also indicate a shift in relative rates of exposure of different age groups to contaminated vehicles.

In many outbreaks, the cause was a relatively uncommon serotype, which points to the importance of serotyping Salmonella. Recent application of molecular biologic techniques to epidemiologic studies has assisted in providing means of identifying outbreaks caused by common serotypes, and further uses of these techniques are currently being evaluated. In this way, the surveillance data will serve as indicators of the effectiveness of various public health control measures.

References

  1. Taylor DN, Wachsmuth IK, Shangkuan Y-H, et al. Salmonellosis associated with marijuana: a multistate outbreak traced by plasmid fingerprinting. N Engl J Med 1982;306:1249-53.

  2. CDC. Multiple outbreaks of salmonellosis associated with precooked roast beef--Pennsylvania, New York, Vermont. MMWR 1981;30:569-70.

  3. CDC. Multistate outbreak of salmonellosis caused by precooked roast beef. MMWR 1981;30:391-2.

  4. Riley LW, Cohen ML. Plasmid profiles and Salmonella epidemiology. Lancet 1982;1:573. Letter.



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