Minnesota Department of Health (MDH) Bug Bytes

July 12, 2002
Vol. 3: No. 9

Topics in this Issue:
1. Salmonella Newport
2. Cow for Lease (Campylobacter Included)
3. VRSA Has Arrived
4. Bug Repellents
5. Arboviral Reporting and Testing
6. Immunization Rule Changes
7. Mark Your Calendar for Emerging Infections Conference

1. Salmonella Newport
The June 28 MMWR (at http://www.cdc.gov/mmwr/preview/
) described the emergence of multidrug-resistant (MDR) strains of Salmonella Newport. In 2001, S. Newport was the third most common serotype of Salmonella in the U.S. and the fourth most common in Minnesota (following Typhimurium, Enteritidis, and Heidelberg). The number of S. Newport cases nationally increased from 5% of Salmonella infections in 1998 to 10% in 2001. This increase in S. Newport infections appears to be associated with the emergence MDR strains of S. Newport.

Highly multidrug-resistant strains of S. Newport emerged in 1999 and have been identified across the U.S. In 2001, 33 (26%) of 128 S. Newport isolates tested nationally were MDR. These S. Newport isolates are resistant to at least nine of 17 antimicrobial agents tested, including amoxicillin/clavulanate, ampicillin, cefoxitin, ceftiofur, cephalothin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline. Of particular concern is that these isolates also show resistance to ceftriaxone, a third generation cephalosporin that is a treatment of choice for invasive Salmonella infections in children. MDR Salmonella infections have been associated with increased hospitalization rates, morbidity, and mortality. Persons infected with MDR S. Newport who need therapy may be treated with fluoroquinolones, or if susceptible, with trimethoprim-sulfamethoxazole.

We have identified similar trends among Minnesota residents from 1994-2000. The proportion of S. Newport isolates that were MDR increased significantly from 2% during 1994-8 to 33% in 2000. Resistance to ceftriaxone was first detected in 1999, and was found in 12 of 56 (21%) isolates from 1999 and 2000.

Data from U.S. outbreak investigations suggest that cattle, particularly dairy cattle, may be a source for human MDR S. Newport. In 2001-2 several outbreaks of MDR S. Newport occurred and were associated with dairy farms, ill cattle, cheese made from unpasteurized milk, and raw or undercooked ground beef. With CDC FoodNet, MDH began a 12-month prospective case-control study in April 2002 to identify the sources of and risk factors for sporadic human S. Newport infections.

Thanks to those of you who send in Salmonella isolates to MDH - the antimicrobial susceptibility testing and pulsed-field gel electrophoresis (PFGE) subtyping of isolates that we do here, and at CDC, makes the recognition of emerging problems such as this possible.

2. Cow for Lease (Campylobacter Included)
Also in the June 28 MMWR was an article about a recent outbreak of Campylobacter jejuni gastroenteritis in northwestern Wisconsin among persons who drank unpasteurized milk obtained from a local dairy farm. Seventy-five cases were identified. It is illegal to sell unpasteurized milk in Wisconsin; this regulation was circumvented through a program in which where customers would pay an initial fee to lease a part of a cow (apparently at least one quarter of an udder) and subsequently receive the unpasteurized milk.

Campylobacteriosis outbreaks due to consumption of unpasteurized milk are not unusual. In Minnesota, we've had such outbreaks (albeit smaller) in each of the past two years. Because of the risk of infection with Campylobacter, as well as E. coli O157, Salmonella (see above article on Salmonella Newport), and Listeria, we of course fervently recommend against the consumption of unpasteurized milk/milk products. This is particularly important for children, the elderly, pregnant women, and others with compromised immune systems.

3. VRSA Has Arrived
In last week's MMWR was a report of the first case of Staphylococcus aureus infection with high-level resistance to vancomycin (VRSA; defined as MIC > 32: this patient's isolate had an MIC>128)(at http://www.cdc.gov/mmwr/preview/
). This 40-year old Michigan patient was receiving outpatient renal dialysis. The arrival of VRSA has been anticipated since the first case of S. aureus with intermediate resistance (MIC=8 g/mL) to vancomycin (VISA) was reported in Japan in 1996. Eight VISA patients have been identified in the U.S. since that time, including one case in Minnesota. Investigations of these cases did not identify transmission of VISA to other patients or healthcare workers. CDC has developed interim guidelines for prevention and control of staphylococcal infection associated with reduced susceptibility to vancomycin (at http://www.cdc.gov/mmwr/preview/

The VRSA isolate contained the vanA vancomycin resistance gene. VanA is one of the resistance determinants that may be present in vancomycin-resistant enterococcus (VRE). It is possible that the S. aureus strain in this case acquired vancomycin resistance through the exchange of genetic material from VRE (this patient had VRE isolated from a foot ulcer). Although such exchange has been demonstrated in vitro, this is the first time that a vancomycin resistance determinant has been identified in a S. aureus isolate. This case emphasizes the importance of antimicrobial stewardship and adherence to recommended infection control practices.

NCCLS guidelines recommend sending all S. aureus isolates with a vancomycin MIC of > 4 g/mL to a reference laboratory. In Minnesota all such isolates should also be sent to us, which will serve as the reference lab with no charge for this service. MIC determinations by broth or agar dilution, or by Etest are the "gold standard" for vancomycin susceptibility. If you have any questions about vancomycin susceptibility testing in S. aureus please call Billie Juni at 612-676-5938.

4. Bug Repellents
In last week's New England Journal of Medicine was a report of a study comparing various insect repellents (abstract available to non-subscribers at http://content.nejm.org/cgi/content/short/347/1/13). Human volunteers placed their arm in a cage with 10 female mosquitoes under controlled laboratory conditions. Sixteen different repellents were tested; those containing DEET (N, N-diethyl-3-methylbenzamide) provided protection for the longest time. Given the likely large, increase in the mosquito population in Minnesota over the next several weeks, this is useful, timely, practical information to share. Repellents containing DEET continue to be the most effective ones available.

5. Arboviral Reporting and Testing
Speaking of bugs, in Minnesota, arboviral encephalitis cases are reported from June through September, but most occur in late July through August. We have no evidence of West Nile virus (WNV) in the state to date; however, several endemic arboviruses could cause illness this summer (LaCrosse encephalitis, Western equine encephalitis, and Eastern equine encephalitis). At the time this Bug Bytes is going to press North Dakota has announced that a horse from Grand Forks has tested positive for WNV; it developed symptoms on June 30.

We have an arbovirus panel available, and we encourage physicians who see suspect cases of arboviral encephalitis to submit clinical samples to us for testing. Please call us at 651-201-5414 or 1-877-676-5414 to report your suspect cases and to arrange arboviral testing. We have several tests available for human samples:

  • WNV: IgM antibody capture ELISA, IgG ELISA (note: positive tests will be forwarded to CDC for neutralization test confirmation)
  • LaCrosse encephalitis, Eastern equine encephalitis, Western equine encephalitis, and St. Louis encephalitis: IgM IFA
  • We encourage the collection of both acute and convalescent (approximately 2-4 weeks after acute sample) samples

Cerebrospinal fluid:

  • WNV and endemic arboviruses: TaqMan assay, Vero cell culture

6. Immunization Rule Changes
We are considering changes to the child care and school immunization requirements including requiring varicella vaccine for children in child care, kindergarten and seventh grade, and pneumococcal and hepatitis B vaccines for children in child care. Public hearings will be held including one on July 24 5:30 - 8:00 p.m. More information is at http://www.health.state.mn.us/divs/dpc/

7. Mark Your Calendar for Emerging Infections Conference
Once again we are co-sponsoring the "8th Annual Emerging Infections in Clinical Practice and Emerging Health Threats Conference". The conference will be on Friday November 15 in Minneapolis. We will have some great speakers and presentations this year including Dr. Marci Layton, New York City Assistant Commissioner of Health speaking on the medical and public health response to terrorism; Dr. Philip Tarr, University of Washington School of Medicine, on the medical management of E. coli O157:H7; Dr. Cynthia Whitney, CDC, on pneumococcal disease; and Dr. Scott Fridkin, CDC, on resistant S. aureus in the community and in healthcare settings. Registration will be available soon through University of Minnesota Continuing Medical Education.


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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Updated Friday, November 19, 2010 at 02:16PM