Restaurant-Associated Outbreak of Typhoid Fever Traced to a Chronic Carrier – Colorado, 2015

BACKGROUND: Typhoid fever (infection with Salmonella Typhi) is common in developing countries, but rare in the United States, where reported infections are usually sporadic and internationally-acquired. Humans are the only reservoir for S. Typhi; disease is transmitted through fecal-oral routes. The incubation period is 3–60 days and asymptomatic carriage occurs in 2-5% of cases, making investigation challenging. During October 2015 two unrelated, non-travel associated typhoid fever cases from the same county were reported to the Colorado Department of Public Health and Environment. We sought to identify additional cases, determine risk factors, and implement control measures.

METHODS:  We defined a case as a person with clinically-compatible illness from whom S. Typhi with one of two outbreak pulsed-field gel electrophoresis (PFGE) patterns was isolated between July 1 – October 15, 2015. A carrier was a person who reported no recent illness and had S. typhi with an outbreak PFGE pattern isolated from stool. We searched for additional cases through passive reporting, the PulseNet database, and two Health Alert Network broadcasts distributed to clinicians. To determine common case exposures we interviewed cases, reviewed credit card statements and social media for restaurant exposures, and examined loyalty card records for grocery purchases. We conducted an environmental assessment at Restaurant A. We attempted to obtain two stool cultures from all current workers at Restaurant A and former workers present during the cases’ exposure period (August 10-20, 2015). 

RESULTS:  Three cases were identified. Two (67%) were hospitalized; all recovered. All cases ate at Restaurant A during August16 ̶ August 20, 2015. The state public health laboratory cultured 70 worker specimens. One Restaurant A food handler tested positive for S. Typhi, denied any recent illness, and was classified as a carrier. He was born in an endemic country and had last traveled outside of the US 15 years prior. He was excluded from work and treated with 28 days of azithromycin; follow-up testing is in progress. The environmental assessment did not reveal deficiencies in hand hygiene or other food handling issues.

CONCLUSIONS:  This outbreak demonstrates the potential for chronic typhoid carriers to cause illness in others, even many years after infection. When non-travel associated cases of typhoid fever are detected, rapid and thorough interviewing is essential; social media posts and credit card receipts can be useful. Open collaboration between local public health, state public health, public health laboratories, cases, and industry is imperative for successful investigations.