in august 2004 , mdh was notified of 2 previously healthy 15-year - old male patients who were hospitalized for septic arthritis caused by mrsa ; 1 had required treatment in an intensive care unit .
the patients had been in the same group that participated in a 21-day wilderness canoe trip in northern minnesota , usa . a third case - patient ,
a previously healthy 17-year - old female camper who had participated in an earlier 21-day trip and had had a skin infection without complications , was identified during the investigation ( table ) .
a case was defined as a clinically relevant , culture - confirmed , mrsa infection that occurred between june 1 and september 30 , 2004 , in a staff member , camper , or member of a camper 's household .
colonization was defined as mrsa identified from the nares of these persons in the absence of mrsa infection .
mdh and local public health staff investigated the base camp . during the 21-day canoeing trip
, participants spent 1 day at base camp at the beginning and end of the trip ; the remaining time was spent canoeing , portaging , and camping on the trail .
campers and guides shared a common tent and did all activities together , but each had his or her own sleeping bag and towels .
campers and guides did not have access to running water or soap outside of base camp ; the information on the wilderness area permit discourages use of soap , including biodegradable soap , within 150 feet of water .
campers who had participated in the same , concurrent , or preceding canoe trips with the same itinerary and their household members were interviewed regarding health history , skin infections and injury , hygiene , clothing , camping behavior , and contact with other campers .
swabs of anterior nares were obtained from consenting staff , campers , and members of campers ' households and were submitted to the mdh public health laboratory .
susceptibility testing was conducted by broth microdilution ( pml microbiology , wilsonville , or , usa ) and interpreted according to clinical and laboratory standards institute ( formerly nccls ) criteria .
pulsed - field gel electrophoresis ( pfge ) was performed by digestion with the restriction enzyme smai ( 7 ) .
patterns were compared visually and with bionumeric software ( applied maths , kortrijk , belgium ) to reference strains of s. aureus ( 8) .
sequences encoding toxin genes ( tsst-1 , panton - valentine leukocidin , sea , seb , sec , and sed ) were detected by pcr ( 9,10 ) .
univariate analysis was conducted with epiinfo version 6.04 ( centers for disease control and prevention , atlanta , ga , usa ) using a significance level of p<0.05 .
all campers reported having had frequent skin injuries , including insect bites , cuts , burns , blisters , and abrasions , during their trips .
campers reported having worn shorts most of the time and frequently having had wet skin , clothing , and shoes .
no differences were identified between campers with and without ca - mrsa or between camping groups with and without ca - mrsa in terms of health history , use of antimicrobial drugs during the past year , skin infections and injury , hygiene , clothing , or camping behavior .
members of 2 households could not be reached , and no information was obtained on the number of persons in these households .
interview responses of household members of case - patients did not differ from those of household members of the other campers and staff .
no case - patient or colonized person reported a history of mrsa infection or colonization .
one camper who was not a case - patient reported having had a positive blood culture for ca - mrsa in the prior year ; this camper had been hospitalized with an infection that began as cellulitis and resulted in septic shock and was found to be not colonized at the time of the investigation . also , the camp director informed mdh that in the prior year , 2 counselors had been treated for apparent spider bites at a local clinic ; however , cultures had not been obtained .
nares swabs were obtained for case - patients 2 and 3 but not case - patient 1 because he was receiving nasal mupirocin treatment .
nares swabs were also obtained for 62% of campers without mrsa infection ; of these , 1 female camper who had participated in a preceding trip was found to be colonized with mrsa .
swabs obtained from the anterior nares of 16 camp guides and base camp staff members showed mrsa colonization in 1 .
this staff member had not gone on any camping trips with the case - patients . of nares swabs from 40 household members ( including all 8 household members of case - patients ) , none was positive for mrsa .
all 5 mrsa isolates ( from the 3 case - patients and the 2 colonized persons ) were susceptible to clindamycin , ciprofloxacin , erythromycin , gentamicin , linezolid , quinopristin / dalfopristin , rifampin , tetracycline , trimethoprim / sulfamethoxazole , and vancomycin and had an mic for mupirocin of < 4 g / ml . the isolates were usa400 pulsed - field type and were indistinguishable by pfge ( 8) . the isolate from the camper who had had an mrsa infection in 2003 was also indistinguishable by pfge .
all 2004 isolates contained genes encoding panton - valentine leukocidin , sea , and sec ( 10 ) . to prevent further infections ,
camp staff were given information about s. aureus , mrsa , and infection - prevention measures .
campers were instructed to wear long pants when possible , protect skin from injury ( e.g. , use insect repellent ) , report all suspected skin infections promptly , keep skin as clean as possible , use alcohol - based hand sanitizers , and not share personal items like towels and clothing . frequently touched surfaces were cleaned with a bleach solution , and life vests were assigned to individual campers and disinfected between campers .
ca - mrsa infections are increasingly reported and can be severe . despite multiple outbreaks attributed to usa300 , only a few reported case clusters have been caused by usa400 ( 11,12 ) .
usa400 does contain virulence factors , and although most cases have been mild skin and soft tissue infections , some have been severe and fatal ( 13 ) .
furthermore , although the colonization rate was low for staff , campers , and household members ( 2.7% ) , it was higher than ca - mrsa colonization rates for the general population ( 14 ) , as would be expected for case - patient contacts . s. aureus ( including ca - mrsa ) spreads easily among people in crowded settings , particularly when adequate hygiene can not be maintained , both of which occurred in this camping setting .
although anecdotal , suspected , and confirmed cases during the prior year are consistent with ongoing transmission associated with the camp , that spider bites were reported is noteworthy because ca - mrsa infections are often misdiagnosed as spider bites ( 15 ) .
injuries and breaks in skin should be closely monitored in settings where medical care is not readily available .
methods for skin protection and hygiene should be developed and implemented for populations in settings where ca - mrsa transmission and infection can be anticipated .
 we investigated a cluster of community - associated methicillin - resistant staphylococcus aureus infections among persons at a wilderness canoe camp . 
 isolates from the investigation had identical profiles for susceptibility , pulsed - field gel electrophoresis , and toxins . 
 participants in activities that involve skin injury , person - to - person contact , and inadequate hygiene are at increased risk for methicillin - resistant s. aureus infections . 
The Study
Conclusions