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Epidemiologic Notes and Reports Typhoid Fever -- Skagit County, Washington
In June and July 1990, an outbreak of typhoid fever occurred in Skagit County, Washington, following a family gathering of 293 people from five states. This report provides a preliminary summary of the investigation of this outbreak by the Skagit County and Washington State departments of health.
Based on interviews of 257 attendees, 17 (6.6%) of these persons developed an illness that met the case definition for probable or confirmed typhoid fever*. Blood cultures were obtained from seven case-patients and from three other symptomatic persons; four of these yielded Salmonella typhi. Stool specimens from nine case-patients and six asymptomatic persons yielded S. typhi. The 17 case-patients ranged in age from 1 to 50 years; eight were male. Fourteen were from Washington, and three, from California. The mean incubation period was 16.1 days (range: 7-27 days); mean duration of illness was 19.7 days (range: 7-35 days). Two case-patients were hospitalized and treated with systemic antibiotics.
The investigation indicated that consumption of three food items served during the gathering was associated with risk for illness. A foodhandler who prepared one of the implicated food items had an S. typhi-positive stool culture and an elevated antibody titer (1:80) to the Vi antigen, suggesting chronic carriage of S. typhi. No other suspected carriers were identified.
To prevent secondary transmission of S. typhi associated with this outbreak, the county and state health departments implemented several measures from July 30 to August 17, including
Editorial Note: Although the incidence of typhoid fever has declined in developed nations, sporadic cases and outbreaks continue to occur. About 400 cases are reported annually in the United States, and the case-fatality rate ranges from 1.3% to 8.4% (1). In addition to the outbreak in this report, in 1990, state health departments have reported five other outbreaks of typhoid fever to CDC, including two outbreaks associated with restaurants, one with home-prepared food, one with imported shellfish, and one with unknown source. In comparison, from 1980 to 1989, only six outbreaks were reported to CDC.
Because complications of typhoid fever can be life-threatening, outbreaks require immediate and thorough epidemiologic investigation. However, these investigations are often constrained by three factors: 1) identification of outbreaks is often delayed because of the long incubation period (typically 10-14 days); 2) case-finding may be hampered because the symptoms of typhoid fever are similar to those of other illnesses, such as urinary tract or respiratory tract infections (2); and 3) cultures of stool alone often fail to detect the organism (1,3). The probability of recovering the organism can be increased by culturing whole stool samples (rather than rectal swabs), blood, and bone marrow (1,3). Cultures of urine usually are not necessary.
Because outbreaks of typhoid fever are often traced to foodhandlers who are asymptomatic carriers, stool samples from all foodhandlers associated with an outbreak should be cultured, even when the foodhandlers are asymptomatic. However, isolation of S. typhi from the stool of a foodhandler does not necessarily identify that person as the source of the outbreak or as a carrier because the foodhandler may have consumed the contaminated food or drink. To be considered a carrier, a person must excrete the organism for at least 3 months (1). During that time, the potential carrier should be excluded from foodhandling. As demonstrated in this report, testing a possible carrier's serum for antibody to the purified Vi antigen may be helpful because carriers often have a high serum antibody titer (4,5). Therefore, serum specimens should be obtained from all potential or suspected carriers at the time of the investigation and, if possible, repeated several weeks later. The Vi antibody also serves as a useful marker during treatment of chronic carriers because they usually revert to seronegative after successful antimicrobial therapy (6).
A 6-week course of ampicillin with probenecid has been successful for treating chronic carriers with normal gallbladders and without evidence of cholelithiasis (7). A prolonged course of amoxicillin has been reported to be effective even in patients with gallstones or nonfunctioning gallbladders (8). Other effective treatments include trimethoprim-sulfamethoxazole (9) and oral quinolones (10,11). Cholecystectomy is also useful in eradicating the carrier state and may be necessary for patients whose illnesses relapse after therapy or who cannot tolerate antimicrobial therapy (12).
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2. Klotz SA, Jorgensen JH, Buckwold FJ, Craven PC. Typhoid fever: an epidemic with remarkably few clinical signs and symptoms. Arch Intern Med 1984;144:533-7.
3. Gilman RH, Terminel M, Levine MM, Hernandez-Mendoza P, Hornick RB. Relative efficacy of blood, urine, rectal swab, bone-marrow, and rose-spot cultures for recovery of Salmonella typhi in typhoid fever. Lancet 1975;1:1211-4.
4. Engleberg NC, Barrett TJ, Fisher H, Porter B, Hurtado E, Hughes JM. Identification of a carrier by using Vi enzyme-linked immunosorbent assay serology in an outbreak of typhoid fever on an indian reservation. J Clin Microbiol 1983;18:1320-2.
5. Lin FY, Becke JM, Groves C, et al. Restaurant-associated outbreak of typhoid fever in Maryland: identification of carrier facilitated by measurement of serum Vi antibodies. J Clin Microbiol 1988;26:1194-7.
6. Nolan CM, Feeley JC, White PC, Hambie EA, Brown SL, Wong KH. Evaluation of a new assay for Vi antibody in chronic carriers of Salmonella typhi. J Clin Microbiol 1980;12:22-6.
7. Phillips WE. Treatment of chronic typhoid carriers with ampicillin. JAMA 1971;217:913-5.
8. Nolan CM, White PC. Treatment of typhoid carriers with amoxicillin. JAMA 1978;239:2352-4.
9. Pichler H, Knothe H, Spitzy KH, Vielkind G. Treatment of chronic carriers of Salmonella typhi and Salmonella paratyphi B with trimethoprim-sulfamethoxazole. J Infect Dis 1973;128 (suppl):S743-4. 10. Rodriguez-Noriega E, Andrade-Villanueva J, Amaya-Tapia G. Quinolones in the treatment of Salmonella carriers. Rev Infect Dis 1989;11(suppl 5):S1179-85. 11. Gotuzzo E, Guerra JG, Benavente L, et al. Use of norfloxacin to treat chronic typhoid carriers. J Infect Dis 1988;157:1221-5. 12. Mandell GL, Douglas RG, Bennett JE. Principles and practice of infectious diseases. 3rd ed. New York: Churchill Livingstone, 1990:1707-9.
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