Laboratory-based surveillance of paratyphoid fever in the United States: Travel and antimicrobial resistance

Background. The incidence of paratyphoid fever, including paratyphoid fever caused by antimicrobial-resistant strains, is increasing globally. However, the epidemiologic and laboratory characteristics of paratyphoid fever in the United States have never been studied. Methods. We attempted to interview all patients who had been infected with laboratory-confirmed Salmonella serotypes Paratyphi A, Paratyphi B, or Paratyphi C in the United States with specimens collected from 1 April 2005 through 31 March 2006. At the Centers for Disease Control and Prevention (CDC), isolates underwent serotype confirmation, antimicrobial susceptibility testing, and pulsed-field gel electrophoresis typing. Results. Of 149 patients infected with Salmonella Paratyphi A, we obtained epidemiologic information for 89 (60%); 55 (62%) of 86 were hospitalized. Eighty-five patients (96%) reported having travel internationally, and 80 (90%) had traveled to South Asia. Of the 146 isolates received at the CDC, 127 (87%) were nalidixic acid resistant; nalidixic acid resistance was associated with travel to South Asia (odds ratio, 17.0; 95% confidence interval, 3.8-75.9). All nalidixic acid-resistant isolates showed decreased susceptibility to ciprofloxacin (minimum inhibitory concentration, >= 0.12 mu g/mL). Of 49 patients infected with Salmonella Paratyphi B, only 12 (24%) were confirmed to have Paratyphi B when tested at the CDC. Four (67%) of 6 patients were hospitalized, and 5 (83%) reported travel (4 to the Andean region of South America). One case of Salmonella Paratyphi C infection was reported in a traveler to West Africa with a urinary tract infection. Conclusions. Physicians should be aware of the increasing incidence of infection due to Salmonella Paratyphi A and treatment options given its widespread antimicrobial resistance. A paratyphoid fever vaccine is urgently needed. Continued surveillance for paratyphoid fever will help guide future prevention and treatment recommendations.