Minnesota Department of Health (MDH) Bug Bytes
August 5 , 2008
Vol. 9: No. 4
Topics in this Issue:
1. We Take VISA (Reports)
2. Salmonella Serotype Analysis
3. Salmonellosis, Frozen Chicken Entrees, and Microwave Ovens
4. GBS Disease in the Elderly
5. Risk Factors for Meningococcal Disease in High School Students
Increased methicillin-resistant Staphylococcus aureus (MRSA) incidence has lead to greater reliance on vancomycin. The vancomycin MIC level required to inhibit S. aureus is 0.5–2μg/mL. S. aureus that have developed resistance to vancomycin are called vancomycin-intermediate (VISA) or vancomycin-resistant S. aureus (VRSA), as detected and defined according to Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS) approved standards and recommendations (Minimum Inhibitory Concentration [MIC]=4-8 µg/ml for VISA and MIC≥16 µg/ml for VRSA).
Patients at risk for VISA and VRSA have several underlying health conditions such as diabetes, end-stage renal disease, and previous infections with MRSA, or recent hospitalizations, or recent exposure to vancomycin.
Two unrelated cases of VISA infection were recently reported to us. Prior to this, we had confirmed only one VISA case, in 2000. CDC first reported VISA in 1997, and since has reported approximately 100 U.S. cases. The three Minnesota cases had a history of diabetes, non-healing MRSA-positive leg ulcers, and end-stage renal disease requiring renal dialysis. The median age was 59 years, two were males, and one survived. All had a history of vancomycin use, though the length of exposure varied from a few days to several weeks.
CDC reports that all VISA isolates have been MRSA, most were linezolid-susceptible, and most had decreased susceptibility to daptomycin. VISA/VRSA infections are rare and reportable. Contact us immediately and submit isolates for confirmatory testing. If VISA/VRSA is detected, institute infection control precautions including contact precautions with use of gown/gloves for all room entries. Consult an infectious disease specialist regarding antimicrobial therapy. Infection control recommendations and laboratory detection guidelines are available at: http://www.cdc.gov/ncidod/dhqp/ar_visavrsa.html
Non-typhoidal salmonellae cause an estimated 1.4 million illnesses in the United States annually with more than 15,000 hospitalizations and 400 deaths. We co-authored a recent (July 1) paper in the Journal of Infectious Diseases examining data from over 46,000 cases of Salmonella infections from Minnesota and the 10 other Emerging Infections Program (EIP) FoodNet sites during 1996–2006. This was the largest study of Salmonella ever conducted.
Among 46,639 cases, 687 serotypes were identified. Overall, 89% were from stool specimens, 5% were from blood, and 4% were from urine; 22% of the cases were hospitalized, and there were 219 deaths. The most common serotype was S. Typhimurium at 23% of all cases. The case fatality rate for S. Newport (0.3%) was significantly lower than for S. Typhimurium (0.6%); S. Dublin (3.0%) was higher. Thirteen serotypes had a significantly higher proportion of invasive disease than S. Typhimurium (6%), including S. Enteritidis (7%), S. Heidelberg (13%), S. Choleraesuis (57%), and S. Dublin (64%); 13 serotypes were significantly less likely to be invasive. Twelve serotypes including S. Enteritidis (21%) and S. Javiana (21%), were less likely to cause hospitalization than S. Typhimurium (24%); S. Choleraesuis (60%) and S. Dublin (67%) were significantly more so.
A recent University of Minnesota epidemiology graduate student, a member of our “Team Diarrhea”, examined Minnesota Salmonella data alone for 1996-2007 (7,654 cases; median case count of 632). Highest incidence was among those <1 year and 1-4 years of age. Incidence peaked during summer months. Interestingly, there were no urban-rural differences in incidence. Over the study period there was a modest but significant overall decrease in incidence, with a slight increase in 2006-2007.
Because Salmonella serotyping results are generally not available to clinicians in a timely fashion, if at all, initial patient management decisions are made in the absence of such information. However, these data show that salmonellae are closely related genetically yet differ significantly in their pathogenic potentials. Understanding the responsible pathogen mechanisms and host factors may lead to a better understanding of the invasiveness of intestinal bacterial infections.
In an upcoming issue of the Journal of Food Protection will be an article authored by us documenting an emerging problem of salmonellosis associated with frozen stuffed chicken products. During 1998-2006, we investigated four salmonellosis outbreaks associated with raw, frozen, microwaveable, breaded and pre-browned, stuffed chicken products. In 1998, 33 Salmonella Typhimurium cases were associated with a single brand of Chicken Kiev. In 2005, four S. Heidelberg cases were associated with a different brand and variety (Chicken Broccoli and Cheese). During 2005-2006, 27 S. Enteritidis cases were associated with multiple varieties of similar products, predominately of the same brand involved in the 1998 outbreak. In 2006, three S. Typhimurium cases were associated with the same brand of product involved in the 2005 S. Heidelberg outbreak. The outbreak serotype and PFGE subtype of Salmonella was isolated from product in each outbreak.
In these outbreaks, most cases thought that the product was pre-cooked due to its breaded and pre-browned nature, most used a microwave oven, most did not follow package cooking instructions, and none took the internal temperature of the cooked product. Similar to previous salmonellosis outbreaks associated with raw, breaded chicken nuggets or strips in Canada and Australia, inadequate labeling, consumer responses to labeling, and microwave cooking were the key factors in the occurrence of these outbreaks. Modification of labels, verification of cooking instructions by the manufacturer, and notifications to alert the public that these products contain raw poultry, implemented because of the first two outbreaks, did not prevent the other outbreaks. Microwave cooking is not recommended as a preparation method for these types of products, unless they are pre-cooked or irradiated prior to sale. We have been working with distributors and manufacturers of these products on to further improve the labeling and instructions to consumers that they should not use microwaves to cook these raw products.
Group B Streptococcus (GBS) causes invasive infections, particularly at extremes of age (see July 29 issue of Bug Bytes). We conduct population-based surveillance for invasive GBS disease as part of our Emerging Infections Program (EIP) Active Bacterial Core Surveillance (ABCs) project. We collect all isolates and conduct susceptibility testing; serotyping is conducted at CDC.
During 2003-2007, 723 GBS cases were reported among persons > 65 years of age; 126 (17%) among long term care facility (LTCF) residents. Incidence in LTCF residents (67.1 cases/100,000) was three times higher than in the community (21.4 cases/100,000). Overall mortality rate was 6.8% and was similar in both groups. Most cases (84%) had positive blood cultures only. Pneumonia was more common among LTCF residents than community elderly (18.3% vs. 9.4%, p=0.004). LTCF residents were more likely to have underlying COPD (11.9% vs. 6.2%, p=0.024). Serotype distribution was similar in both elderly groups; serotype V (35%) was most common. Serotypes Ia, Ib, II, III, IV and V accounted for 90% and 94% of invasive disease among community and LTCF elderly respectively.
All isolates were susceptible to penicillin. Erythromycin susceptibility decreased significantly from 71.4% in 2003 to 58.7% in 2007 (c2 for trend 5.2, p=0.023), clindamycin susceptibility decreased from 85.7% in 2003 to 76.0% in 2007 (c2 for trend 3.6, p=0.057).
An effective multivalent GBS vaccine would be useful, particularly for elderly LTCF residents.
In the March 2008 Pediatric Infectious Disease Journal was an article detailing the results of a case-control study in which we participated. Cases had confirmed meningococcal disease and were enrolled in grades 9-12. We enrolled 10 of the 56 total study cases. For each case-patient up to 4 controls were selected from the case’s homeroom classroom. Risk factors for disease included male gender, upper respiratory infections, marijuana use, and nightclub/disco attendance. It’s unclear if the latter three factors put a student directly at risk or are markers for other exposures. Attending a barbecue/picnic was associated with a lower risk of disease, probably being a marker for behavior and other exposures.
The majority of the infections in this study could have been prevented with the tetravalent meningococcal conjugate vaccine.
Bug Bytes is a combined effort of the Infectious Disease Epidemiology, Prevention and Control Division and the Public Health Laboratory Division of MDH. We provide Bug Bytes as a way to say THANK YOU to the infection control professionals, laboratorians, local public health professionals, and health care providers who assist us.
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