Salmonella bacteremia in Southern Viet Nam

Abstract & Commentary

Synopsis: Multidrug-resistant Salmonella typhi is a frequent cause of community-acquired septicemia in southern Viet Nam. As tourism to this part of southeast Asia increases, typhoid fever should be carefully considered in the differential diagnosis of febrile patients returning from the area. Multidrug resistant strains and potentially high mortality rates associated with them should be of concern to travel medicine practitioners.

Source: Hoa NTT, et al. Trans Royal Soc Trop Med Hyg 1998;92:503-508.

A prospective study of community-acquired septicemia was conducted from mid-1993 to 1994 in southern Viet Nam. Patients were evaluated at the Centre for Tropical Diseases, Cho Quan Hospital, in Ho Chi Minh City. The microbiology, clinical features, and outcome were compared with studies from other developing countries. During this one-year study period, 3783 blood culture sets were obtained from 3365 patients. Five hundred eighteen had positive cultures (15.3%) and the isolate was considered a community-acquired, clinically significant non-contaminant in 437 patients (13%). Anaerobic blood cultures were not performed as a part of this study. The incidence of septicemia detected was 20.4 episodes per 1000 admissions. Gram-negative aerobes (facultative organisms) accounted for 90% of all isolates in documented cases of bacteremia. Salmonella typhi caused 67% (309 cases) and Salmonella paratyphi A accounted for 3%. Seventy percent of S. typhi were multidrug-resistant (MDR-resistant to chloramphenicol, co-trimoxazole, ampicillin, and tetracycline), and 4% were resistant to nalidixic acid. Three patients were co-infected with both S. typhi and Plasmodium falciparum.

The clinical features and outcomes for those patients with Salmonella-associated enteric fever were compared with those of patients with other types of septicemia. The patients with enteric fever were younger than patients with non-enteric fever (median age of 16 years vs 43 years). The median duration of illness before admission was 10 days for enteric fevers, which was longer than the duration of illness for other types of Gram-negative and Gram-positive bacteremia (4-5 days). Thirty-five percent of patients with enteric fever had diarrhea. Severe disease (with shock, impaired consciousness, gastrointestinal bleeding, intestinal perforation, renal failure, or jaundice) developed in 9% of the patients with enteric fever. However, severely ill patients were often admitted to other hospitals in the city. The mortality rate was lower in the patients with enteric fever than the patients with other forms of bacteremia (0.3% vs 23%).

The proportion of community-acquired septicemia due to Salmonella sp. was compared with studies from other developing countries. Salmonella sp. caused an unusually high (72%) proportion of septicemia in Viet Nam. In contrast to the current study, Hoa and associates cited a report on enteric fever in Thai children that had shown a decline of typhoid fever. This trend was attributed to improved hygiene and sanitation as well as the parenteral typhoid vaccination program for children that began in Thailand in 1977.1

Comment by Lin H. Chen, MD

Enteric fever is a major health problem in many developing countries and refers to both typhoid fever and paratyphoid fever. The current study of mostly urban patients from southern Viet Nam shows a strikingly high proportion of Salmonella sp., especially S. typhi, causing community-acquired septicemia. By comparison, a report from Hong Kong showed Salmonella sp. caused 27% of community-acquired septicemia in children, and S. typhi accounted for only one-third of these infections.2 Travelers to southern Viet Nam appear to have a significant higher risk of potentially returning with typhoid fever, particularly given the median duration of illness of 10 days ensuing prior to admission. This is an area of the world where HIV is just beginning to emerge and the proportion of Salmonella-associated bacteremia due to nontyphoidal strains may increase as it has in Africa with the AIDS pandemic.

Epidemics of MDR S. typhi have been reported from numerous countries.3,4 MDR S. typhi has unfortunately been associated with a higher mortality than infection with susceptible strains,3 and it is alarming that a majority of the strains in the current report (70%) were MDR strains. It is also of concern that nalidixic acid-resistance is emerging, since the quinolone antibiotics have been widely and effectively used to treat multidrug-resistant typhoid fever.5

Given the high proportion of septicemia caused by S. typhi, the high percentage of MDR strains, and the emergence of quinolone resistance, travelers to southern Viet Nam should be particularly cautious regarding typhoid fever. Although food and water precautions are the most important preventive measures, an aggressive approach toward typhoid vaccination appears to be warranted for travelers to southern Viet Nam. Unfortunately, even a large inoculum of S. typhi can overcome the protective effects of typhoid vaccines, and typhoid fever should remain high in the differential diagnosis of febrile travelers returning from Viet Nam, even if they have received typhoid vaccine.

References

1. Thisyakorn U, et al. Am J Dis Child 1987;141:862-865.

2. Cheng AFB, et al. J Trop Med Hyg 1991;94:295-303.

3. Bhutta ZA, et al. Rev Infect Dis 1991;13:832-836.

4. Rowe B, et al. Clin Infect Dis 1997;24 (Suppl 1): 106-109.

5. Wain J, et al. Clin Infect Dis 1997;25:1404-1410.