An Evaluation and Comparison of Multidrug-Resistant Salmonella typhimurium DT 104, Salmonella typhimurium Non-DT 104 and All Other Salmonellosis in Virginia, July 1998 – December 2000
Seth Levine
Introduction: Salmonellosis is a food borne enteric bacterial disease that according to the CDC affects up to four million Americans a year and kills five hundred. Usually symptoms including headache, abdominal pain, diarrhea, nausea and vomiting are self-resolving and do not require treatment. Certain groups such as the young, elderly and immunocompromised, are prone to acquiring more serious infections and should receive antibiotic therapy. However recently it has been discovered worldwide that a new drug resistant strain of salmonellosis is increasing in incidence. Salmonella typhimurium, one of the most common types of Salmonella has built resistance to multiple antibiotics. This strain, known as Salmonella typhimurium definitive type 104 (STDT 104), is resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides and tetracycline. STDT 104 poses a threat to those people with serious infections requiring antibiotics. A descriptive study was performed to determine if STDT 104 rates have increased in Virginia during the last two and a half years.
Objective: This study described the epidemiology of three populations with different disease outcomes. The general characteristics of STDT 104, Salmonella typhimurium Non-DT 104 and all other types of salmonellosis were measured in relation to person (age, sex, race) place (region, county) and time (month to month) from July 1998 – December 2000. State incidence rates, relative risks and trends (month to month) were measured among the three groups.
Methods: STDT 104 data was compiled by the Division of Consolidated Laboratory Services (DCLS – state lab for Virginia) during July 1998 – December 2000. This data was merged with Virginia Department of Health (VDH) data. DCLS cases were categorized based on genetic profiling (Pulsed Field Gel Electrophoresis or PFGE) and drug sensitivity testing including ampicillin, chloramphenicol, streptomycin, sulphonamides and tetracycline. Salmonella cases were separated into three groups using NETSS – Epi Info, Version 6.0. Using Virginia population statistics, proportions, category-specific incidence rates per 100,000 people (95% CI) and relative risks (95% CI) were calculated among the three groups and illustrated in Microsoft Excel. Graphs presenting monthly and seasonal data among the three Salmonella groups were also shown.
Results: STDT 104 incidence rates appeared to remain relatively constant in Virginia from July 1998 –December 2000. In 1998 and 1999, STDT 104 rates were 1.1 per 100,000 and in 2000 they slightly decreased (0.9 per 100,000). Not much difference was displayed between variables (age, gender, race, region and month of infection) among the STDT 104, S. typhimurium Non-DT 104 and other Salmonella groups. All the Salmonella groups had higher incidence rates and RR among the <1 and 1-9 age groups, however this especially held true for the STDT 104 group (higher RR than other groups). The one divergence among the groups appeared to be a greater risk of developing STDT 104 among African Americans {RR = 3.1 (95% C.I. = 2.2-4.4)}. This risk for the African American population did not exist in the S. typhimurium Non-DT 104 group {RR = 1.1 (95% C.I. = 0.8-1.5)} or the other Salmonella group {RR = 1.2 (95% C.I. = 1.0-1.4)}.
Conclusion: Incidence of Salmonella typhimurium DT 104 does not appear to be increasing in the Virginia population within the period of July 1998 – December 2000. Several groups stood out as having an increased risk of developing the disease including young children and the African-American population. Further research is necessary to explain the increased risks among certain groups. More prudent use of antimicrobial agents in feed animals as well as decreasing consumption among the human population might significantly diminish the sum of Salmonella typhimurium DT 104 seen worldwide.
