Minnesota Department of Health (MDH) Bug Bytes
March 30, 2010
Vol. 11: No.2
Topics in This Issue:
1. Bearded Dragons Muck the Potluck
2. Dragons to Frogs
3. Rabies Vaccine Recommendations Change
4. Cryptosporidiosis Rapid Assay Tests
5. Pneumococcal Conjugate Vaccine 13 Approved
We recently investigated an outbreak of Salmonella subspecies IV, an extremely rare subspecies that is primarily reptile-associated. In early December, we detected 3 human isolates with the same PFGE pattern. The 3 cases were from two different households. All had attended a scout troop potluck dinner and had symptom onset 12-24 hours after the potluck. None had reptile contact.
We interviewed potluck attendees and found 19 persons to be ill for an attack rate of 29%. Of the 19 cases, 17 were primary cases and 2 were secondary cases (exposed to a primary case); 5 were stool culture-confirmed. Five had sought health care. Consuming turkey gravy at the potluck was the only food item statistically associated with illness.
The person who prepared the gravy (and turkeys) did so during the 3 days preceding the potluck. She reported having two pet bearded dragons at home. The gravy was never brought to a boil and drippings were added over several days. We visited her home and took environmental swabs. We found multiple swabs positive for Salmonella Labada, a rare serotype, including inside and outside the dragons' terrarium, a dragon's stool sample, a cloacal swab from a dragon (a fun activity!), bathroom sink, and kitchen sink. Because Salmonella shedding by the dragons may be intermittent, we swabbed the contents of the vacuum cleaner bag, thinking it might reflect contamination at the time of the food preparation, and from there we did isolate Salmonella subspecies IV of the same PFGE subtype.
The dragon owner also helped prepare mashed potatoes in a second household where there were 2 culture-confirmed cases including 1 case who did not attend the potluck but only ate leftover mashed potatoes. The potluck food and potatoes were likely contaminated by either the dragons' owner who was asymptomatically infected (a stool sample was not obtained from her) or from contaminated unsanitary kitchen surfaces and equipment from her kitchen.
Jumping from reptiles to amphibians, a recent (January 10) MMWR article reported on a multistate Salmonella Typhimurium outbreak, including 1 Minnesota case, associated with frogs. Beginning April 2009, the Utah Department of Health initially identified 5 cases with indistinguishable PFGE patterns, predominantly among children. To date, there have been 111 cases from 31 states. Among the cases, 53% were female; median age was 5 years (range: 3 weeks-73 years), and 77% were aged <10 years. Among cases with outcome information available, 34% had been hospitalized; no deaths were reported.
In a multistate case-control study, exposure to pet frogs was found to be significantly associated with illness. Among 14 cases who knew the type of frog, all had exposure to an exclusively aquatic frog species, the African dwarf frog. Environmental samples from the frog aquariums in 4 cases' homes yielded S. Typhimurium isolates matching the outbreak strain. Traceback information indicated these frogs came from the same California breeder. This is the first reported multistate outbreak of Salmonella infections associated with amphibians.
When asked about potential for Salmonella infection, about half reported awareness of association between contact with reptiles and Salmonella, but only 11/36 reported awareness of association with amphibians. Among 20 cases from whom information was available, the frog's aquarium was cleaned in the kitchen sink in the homes of 6 cases, and in the bathroom sink in the homes of 7 others.
The most likely outbreak source was contact with water from the frogs' aquariums. Because African dwarf frogs are small and rest at the aquarium bottom where children have difficulty reaching them, direct handling as the source of transmission is less likely. Amphibians are known carriers of Salmonella. African dwarf frogs are purely aquatic animals, typically <2 inches long from nose to tail stub, and sold as aquarium pets. In one study, 21% of aquarium frogs tested from 16 retailers were positive for Salmonella. Salmonella shed from frogs is readily recoverable from aquarium water where frogs are housed.
The Minnesota case was an adult woman who had illness onset in August. She was interviewed four times over several months, and was asked in late November about exposure to frogs when she then recalled purchasing African dwarf frogs in the month prior to her illness; her frogs were no longer alive for testing.
Anecdotal reports suggest persons buy frogs as an alternative to pet turtles because of concern over salmonellosis. Public education regarding the risk for illness associated with turtles and other reptiles should be expanded to include the risk from pet frogs and other amphibians. Children aged <5 years might be less likely to consistently practice proper hand hygiene, so prevention and control measures should be emphasized for this age group.
The Advisory Committee on Immunization Practices (ACIP) now recommends a 4-dose vaccine schedule for postexposure prophylaxis (PEP) to prevent human rabies instead of 5 doses as has been the case for the last 30 years. The ACIP reviewed experimental animal studies, human clinical studies, and epidemiologic surveillance data, all of which suggested that 4 doses provide full immunity and that the fifth dose is does not increase protection. For previously unvaccinated persons potentially exposed to rabies, the new regimen is wound cleansing followed by four 1-ml doses of human diploid cell vaccine (or purified chick embryo cell vaccine) on days 0, 3, 7, and 14. On day 0, 20 IU/kg body weight of human rabies immune globulin should also be administered, infiltrated around the wound site if anatomically feasible. The elimination of the fifth dose is estimated to save over $16.5 million in U.S. health care costs. Note the regimen remains at 5 doses for those with immunosuppression, and that the rabies vaccine package inserts may still list the 5-dose regimen instead of these new recommendations.
Learn more about: Rabies>>
In a paper just published (April 15 CID) we reported on an evaluation of rapid assays used by Minnesota clinical laboratories for the diagnosis of cryptosporidiosis. Cryptosporidiosis incidence has been generally increasing and it may be due to an increase in diagnostic testing. Minnesota labs are required to submit clinical materials from positive specimens to us for confirmatory testing; 179 specimens from 235 reported cases were submitted in 2008. We tested them by PCR, and if the results were negative, they were tested by MERIFLUOR DFA and the modified Ziehl-Neelson stain. The overall positive predictive value for rapid tests was 56% (34% in January-May, a low prevalence season; and 69% in June-October, a high prevalence season).
The lower positive predictive values observed may be due to improper storage of test kits, use of unapproved transport media, improper dilution of unpreserved specimens, technician error in performing the test or reading the results, or problems with the antibody in the assays. Laboratories should not use a rapid assay as a screening test in populations with low prevalence of cryptosporidiosis. They should carefully follow sample collection, handling, storage, and test procedures. Even though rapid assays can be used as a screening test in higher prevalence populations, positives still should be confirmed with a more traditional test.
Learn more about: Cryptosporidiosis (Cryptosporidium spp.)>>
On February 24, a 13-valent pneumococcal conjugate vaccine (PCV13 [Prevnar 13]) was licensed by the Food and Drug Administration for prevention of invasive pneumococcal disease (IPD) caused by the 13 pneumococcal serotypes covered by the vaccine (1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F) and for prevention of otitis media caused by serotypes in the 7-valent pneumococcal conjugate vaccine formulation (PCV7 [Prevnar]) which it replaces. PCV13 is approved for use among children aged 6 weeks-71 months. The Advisory Committee on Immunization Practices recommends PVC13 for routine vaccination of all children aged 2-59 months, vaccination of children aged 60-71 months with underlying medical conditions that increase their risk for pneumococcal disease or complications, and vaccination of children who previously received 1 or more doses of PCV7. Details are at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5909a2.htm .
PCV7 has been highly effective in preventing IPD in young children. Following PCV7 introduction, overall rates of IPD in children <5 years old decreased by 80%; rates caused by the 7 serotypes included in the vaccine decreased by more than 99%. Since then, however, rates of IPD caused by other serotypes have increased.
In 2009, there were 98 cases of IPD in Minnesota in children <5 years old, only 1 of that was caused by a serotype included in PCV7, and 68% (65/95 serotyped isolates) that were caused by serotypes additionally covered in the new vaccine. We will be starting an Emerging Infections Program PCV13 vaccine effectiveness study in May 2010.Learn more about: Pneumococcal Disease (Streptococcus pneumoniae)>>
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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