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Back To Vidyya Surveillance Of Infection With Salmonella Typhi

Infection Causes Concern In Europe And The United States

In Europe the main risk factor for infection with Salmonella typhi is travel, particularly to the Indian subcontinent. Similarly, while the levels of resistance to the antibiotics of choice (ciprofloxacin and third generation cephalosporins) are low, resistance can and does occur. Surveillance of salmonellosis, including antimicrobial resistance testing, is needed to monitor the evolution of antimicrobial resistance, and to provide clinicians, public health physicians, and policymakers with up to date information.

The Enter-net international salmonella database for 1999, which includes data from all 15 countries of the European Union plus Switzerland, Australia and the Czech Republic, contains records of 127 278 human cases of salmonellosis, 461 (0.36%) of whom were infected with Salmonella typhi (1). Travel details were recorded for 198 of these cases – Indian subcontinent 114 cases (58%), Papua New Guinea 17 (9%), Indonesia 14 (7%) and Tunisia 13 (7%), other countries six cases or fewer. The results of antimicrobial resistance testing are available for 62 of the 461 cases (table). Eleven cases were resistant to four or fewer antimicrobials, one resistant to five, three to six, and two to seven. Fourteen were designated as fully sensitive, although nine of these were tested against six antimicrobials rather than the range of 11 monitored by Enter-net. The remaining 31 isolates gave intermediate results to at least one of the antimicrobials tested.

  Resistant Intermediate Sensitive No. tested
Ampicillin 9 9 44 62
Chloramphenicol 9 0 53 62
Streptomycin 6 21 23 50
Sulphonamides 9 23 18 50
Tetracycline 10 15 37 62
Trimethoprim 7 1 53 61
Ciprofloxacin 1 0 61 62
Gentamicin 0 0 50 50
Kanamycin 0 1 61 62
Nalidixic acid 5 0 45 50
Cefotaxime 0 0 50 50

Although the risk of acquiring typhoid fever in the United States and other developed countries remains low, drug resistance among Salmonella typhi is increasing. A cross sectional laboratory based surveillance study reported in JAMA estimated the incidence of infections with antimicrobial resistant S. typhi and identified risk factors for infection (2). The results suggest that ciprofloxacin and ceftriaxone are appropriate empirical treatment for suspected typhoid fever, but resistance may be anticipated. Continued monitoring of antimicrobial resistance among S. typhi strains will help determine vaccination and treatment policies.

S. typhi isolates and epidemiological information from 293 people with symptomatic typhoid fever were submitted to US public health departments and laboratories from 1 June 1996 to 31 May 1997. Altogether 228 patients were admitted to hospital for a mean duration of seven days, and two died. In the six weeks before becoming ill, 216 had travelled to India, Pakistan, Bangladesh, or Haiti. Fifty-three patients had acquired typhoid fever in the US. Seventy-four isolates of S. typhi were found to be resistant to one or more antimicrobial agents, 51 showed multidrug resistance to ampicillin, chloramphenicol, and trimethoprim-sulphisoxazole.

Although the number of reported cases of typhoid fever in the US has remained fairly stable for 20 years the sources of infection and patterns of antimicrobial resistance have changed. The proportion of cases attributed to exposure on the Indian subcontinent increased from 25% in 1985 to 57% in the study reported (2). From 1985 to 1989, 0.6% of US strains were reportedly multidrug resistant, compared with 17% in the study reported (2). Foreign born US residents returning to their country of origin and children were identified as the two groups in need of vaccination. The high incidence of infection among travellers to the Indian subcontinent along with the increasing resistance in the strains that they acquire there indicate their particular need of vaccination before travel.

References:

  1. http://www.phls.co.uk/International/Enter-Net/enter-net.htm
  2. Ackers ML, Puhr ND, Tauxe RV, Mintz ED. Laboratory-based surveillance of Salmonella serotype typhi infections in the United States. Antimicrobial resistance on the rise. JAMA 2000; 283: 2668-73. (http://jama.ama-assn.org/issues/v283n20/full/joc91515.html)

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Editor: Susan K. Boyer, RN
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