Most U.S. Typhoid Fever Linked to Foreign Travel

October 2009

A Total Of 47% Of Travel-Related Cases Were In People Who Had Visited India And 10% In People Who Had Visited Pakistan

By Mary Ann Moon
Elsevier Global Medical News

Eighty-five percent of typhoid fever cases in the United States are related to foreign travel, particularly travel in the Indian subcontinent, investigators reported in JAMA.

The proportion of typhoid cases associated with foreign travel has always been high, but it has increased steadily to a new peak during the past few decades, said Dr. Michael F. Lynch and his associates at the Centers for Disease Control and Prevention, Atlanta.

The researchers examined trends in typhoid infections in the United States for 1999-2006 by combining epidemiologic data reported to the CDC's National Typhoid Fever Surveillance System with data on Salmonella ser Typhi isolates sent to the National Antimicrobial Resistance Monitoring System for Enteric Bacteria.

Typhoid fever continues to be an infrequent infection in the United States, but it carries substantial morbidity. Nearly three-quarters of cases reported in the study required hospitalization, which lasted more than 1 week in half of the cases. Three patients--two who acquired the infection in India and one who emigrated from Mexico--died of typhoid.

Analysis revealed that the fraction of travel-associated cases in the United States rose from 64% in 1999 to 85% in 2006. Nearly half of the travel-associated cases (47%) were in people who had recently visited India, another 10% in individuals who visited Pakistan, and another 10% in people who visited Bangladesh. The Philippines, Indonesia, and Cambodia accounted for a total of 7% of cases.

In the past, Mexico was the chief source of foreign typhoid infections in the United States. However, Mexico, Guatemala, El Salvador, and Haiti together accounted for only 13% of cases, while 4% of travelers with typhoid fever had visited Africa.

Only 5% of the 1,094 travelers in the study who reported vaccination status had received any typhoid vaccine within 5 years of their trip. Typhoid vaccines are readily available and well tolerated, the researchers noted, and should be recommended even for travelers whose trips to endemic areas will be shorter than 2 weeks.

"Because neither commercially available vaccine is 100% effective, food and water precautions remain important. Further advice on food and water safety while traveling can be found at ," Dr. Lynch and his colleagues wrote (JAMA 2009;302:859-65).

More than half the cases in the study were reported from three states: California (29%), New York (15%), and New Jersey (7%). Patients' median age was 22 years (range less than 1 year to 90 years).

Of the 391 cases of typhoid fever acquired within the United States, 17% were traced to a typhoid carrier and 22% were part of typhoid outbreaks.

Typhoid strains that were resistant to antimicrobials were common, with multi- drug-resistant strains causing 13% of infections. "Notably, about one-third of all S. Typhi isolates . . . were resistant to the quinolone nalidixic acid, and the proportion of [strains resistant to this drug] among U.S. patients steadily increased during the study period," the researchers said.

Resistance to nalidixic acid is a marker for decreased susceptibility to fluoroquinolones in general. Moreover, most isolates in the study that were resistant to that agent also showed decreased susceptibility to ciprofloxacin.

"Resistance to ampicillin and to trimethoprim-sulfamethoxazole remains prevalent and precludes the use of these agents as initial therapy," the investigators wrote. "A fluoroquinolone remains an appropriate choice for empirical therapy in adults," they added. "Among children, in whom fluoroquinolones are limited to off-label use, third-generation cephalosporins are appropriate."

No financial disclosures were reported for the study.

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