Salmonella typhi infections in the United States, 1975-1984: increasing role of foreign travel.

To explore changes in the epidemiology of typhoid fever in the United States, cases reported to the Morbidity and Mortality Weekly Report (MMWR) and typhoid case report forms submitted by state and local governments are reviewed. The incidence of typhoid fever in the United States fell from one case per 100,000 population in 1955 to 0.2 cases per 100,000 in 1966 and has since remained fairly stable. Review of case report forms for 2,666 cases of acute typhoid fever that occurred between 1975 and 1984 showed that 62% were imported, in contrast to only 33% during 1967-1972. The proportion of cases imported has continued to rise, reaching 69% in 1984. The major sources of the 1975-1984 cases were Mexico (39%) and India (14%). The case-fatality rate was 1.3%. Antimicrobial resistance was a minor problem, and large outbreaks were unusual. Further decline in the incidence of typhoid fever in the United States probably must await the advent of an effective vaccine with minimal adverse effects for use by travelers.

Massive outbreak of antimicrobial-resistant salmonellosis traced to pasteurized milk.

Two waves of antimicrobial-resistant Salmonella typhimurium infections in Illinois totaling over 16 000 culture-confirmed cases were traced to two brands of pasteurized 2% milk produced by a single dairy plant. Salmonellosis was associated with taking antimicrobials before onset of illness. Two surveys to determine the number of persons who were actually affected yielded estimates of 168 791 and 197 581 persons, making this the largest outbreak of salmonellosis ever identified in the United States. The epidemic strain was easily identified because it had a rare antimicrobial resistance pattern and a highly unusual plasmid profile; study of stored isolates showed it had caused clusters of salmonellosis during the previous ten months that may have been related to the same plant, suggesting that the strain had persisted in the plant and repeatedly contaminated milk after pasteurization.

Risk factors for urinary tract infection.

The authors carried out a case-control study in 1982-1983 to investigate the possible influence of behavioral factors on the risk of urinary tract infection. Study participants were college women attending a student health service. Cases were 43 women with culture-confirmed urinary tract infection. There were two control groups: 149 women with upper respiratory infection and 227 women visiting the gynecology clinic. Using each set of controls, the study confirmed that sexual intercourse is a risk factor and that there is a dose-response effect for increasing levels of coital frequency. The study also found that use of the diaphragm was significantly associated with urinary tract infection (odds ratios 3.0, 2.3), an association which remained significant even after controlling for possible confounding by coital frequency. The findings did not show an association with many of the factors commonly believed to be important such as type of clothing worn and volume of fluids consumed.

PIP: A case study was conducted among college women using a student health service at a university in southern Michigan to identify and evaluate behavioral factors which may be determinants of urinary tract infection. Women who presented to the student health service with symptoms suggestive of urinary tract infection and found to have pyuria on urinalysis were offered the opportunity to participate in a clinical trial comparing antibiotic regimens in the treatment of their urinary infection. Women with identified structural abnormalities of the urinary tract were not admitted to the study. On their 1st visit, women enrolled in the antibiotic study were asked to complete a questionnaire for the epidemiologic study described here. Midstream specimens were obtained during the 1st visit prior to therapy and were cultured quantitatively using standard methods. A patient with symptoms of acute urinary tract infection was included as a case if the urine culture was positive or probable. 2 different control groups were used to assess risk factors for urinary tract infection. For the 1st control group, women presenting to the student health service with coryza and/or sore throat, an oral temperature of less than 38.9 degrees Centigrade, and a clinical diagnosis of uncomplicated viral upper respiratory infection were asked to complete the same questionnaire as cases. For the 2nd control group, women attending the gynecology clinic at the same student health service for routine scheduled pelvic examinations and/or contraceptive services were asked to complete the same questionnaire. Cases were entered into the study from March through December 1982. The students used as controls participated from March 1982 through March 1983. The subjects completed a standard self-administered multiple-choice questionnaire, asking primarily about activities during the 3 weeks prior to completion of the questionnaire. 47 women with presumptive urinary tract infection participated in the clinical trial. 43 cases of confirmed urinary tract infection were identified, 38 with a positive and 5 with a probable urine culture result. In all, 149 upper respiratory infection controls and 227 gynecology controls participated. The history of previous urinary tract infection was significantly greater in cases than in either of the control groups. 4 variables were included in the final logistic model: coital frequency within 3 weeks, use of the diaphragm within 3 weeks, history of previous urinary tract infection, and age. Coital frequency during the previous 3 weeks was associated strongly with illness, with generally higher risk at higher frequencies. A significant association with the diaphragm was observed in comparison with both control groups. The findings failed to show an association with many of the factors commonly believed to be important such as type of clothing worn and volume of fluids consumed.

Changes in antimicrobial resistance of Salmonella isolated from humans in the United States.

Changes were examined that occurred in the antimicrobial susceptibility between 1979-1980 and 1984-1985 of Salmonella organisms isolated from humans who resided in a random sample of counties in the United States. Resistance to one or more antimicrobials rose significantly from 16% (82 of 511 isolates) in 1979-1980 to 24% (117 of 485 isolates) in 1984-1985. In addition, statistically significant increases occurred in the proportion of organisms resistant to only one antimicrobial (from 4% to 9%), the rate of resistance of Salmonella typhimurium (from 14% to 26%), and the rate of resistance to tetracycline. For one commonly occurring serotype, Salmonella heidelberg, the proportion of resistant strains fell significantly from 67% in 1979-1980 to 35% in 1984-1985. When epidemiologic characteristics of patients were examined, previous use of antimicrobials for treatment of other illnesses was a significant risk factor for acquiring clinically important infections with antimicrobial-resistant Salmonella. Changes detected in the antimicrobial resistance of Salmonella during this time will ultimately affect the efficacy of antimicrobial therapy in treating human disease.

Salmonellosis outbreak on transatlantic flights; foodborne illness on aircraft: 1947-1984.

In March 1984, 186 cases of gastroenteritis due to Salmonella enteritidis were reported after 29 flights to the United States on an international airline. An estimated 2,747 passengers on flights to the United States were affected. Illness was associated with flying supersonic or first class (odds ratio = 15, p less than 0.001). Eating food from the first-class menu was associated with illness (p = 0.09), and eating a tourist-class entree was protective (p less than 0.01). In 23 reported outbreaks of foodborne illness on aircraft, Salmonella has been the most common pathogen (seven outbreaks), followed by Staphylococcus (five outbreaks), and Vibrio species (five outbreaks). Outbreaks are most often the result of an improper temperature for preparation or for holding food in the flight kitchens. Serving the flight crew meals from one kitchen carries the risk that the entire crew will become ill.