the camp opened july 26 , 2009 ( day 1 ) , with 101 campers and 116 staff . all participants were physically examined and questioned so that anyone with presence of or exposure to potentially communicable diseases could be excluded from attending camp . campers ( 812/patrol ) were grouped in age- and gender - specific patrols ( b1b4 and g1g4 ) with assigned staff ( 45/patrol ) ; they slept in bunkhouses and had common bathing facilities . all campers and staff dined together and shared various activities . on day 2 , fever developed in a healthy camper in patrol g3 and promptly subsided . fever also developed in a second camper ( patrol b2 ) with sickle cell disease ( scd ) . this camper was seen at the local hospital , had a negative rapid influenza test ( rit ) result , and was sent home . on day 3 , fever and cough developed in 4 children ( 2 from b2 ) ; 1 was tested by rit with a negative result . , fever developed in1 child with cancer ( b2 ) and 1 with scd ( g2 patrol ) ; each had positive test results for influenza a virus . the number of episodes of fever was considered excessive , and because additional campers reported having fever the camp was closed . at the time of dismissal , all campers and staff were provided masks and instructions about cough etiquette and handwashing ; a dose of oseltamivir was also administered , and a prescription for oseltamivir was provided . ten days after the camp closed , all attendees were contacted ( by email , telephone , and regular mail ) to gather information about their outcomes . clinical signs and symptoms of interest were fever ( measured or subjective ) or chills ; cough or sore throat ; muscle pain ; and nausea , vomiting , or diarrhea . on the basis of an adaptation of the definition by the centers for disease control and prevention ( www.cdc.gov/h1n1flu/clinicians ) , persons with fever or chills and symptoms in > 2 other categories were classified as having influenza - like illness ( ili ) ; persons with fever alone ( without an explanation ) and symptoms in 1 other category , or no documented fever but symptoms in > 2 other categories , were classified as having probable ili ( p - ili ) . a case - patient was defined as a person in whom ili or p - ili developed within 10 days of closing of the camp . questionnaires were returned by 88 ( 76% ) and 77 ( 76% ) of staff and campers , respectively . mean age was 22.5 ( range 1469 ) years for staff and 10.5 ( range 515 ) years for campers . of 88 staff , 56 reported no chronic medical condition ; a few reported cancer in remission ( n = 7 ) , scd ( n = 3 ) , or other conditions ( n = 22 : 9 asthma , 2 inflammatory bowel disease , 2 unspecified , and 1 each with epilepsy , gall stones , chronic hepatitis c , immune thrombocytopenic purpura , kartagener syndrome , mental retardation , porphyria , stroke , and type 1 diabetes mellitus ) . of 77 campers , 45 ( 58% ) reported no underlying illness , and a few reported cancer ( n = 20 : 12 leukemia , 2 lymphoma , 4 solid organ tumor , 2 unspecified ; 2 were receiving maintenance therapy , the others had completed treatment ) , scd ( n = 8) , or other ( n = 4 : 2 asthma , 1 immune thrombocytopenic purpura , and 1 cardiomyopathy ) . of 165 attendees who returned the questionnaire , 59 ( 38.5% ) reported symptoms : fever ( 40 , 68% ) , cough ( 30 , 51% ) , sore throat ( 21 , 36% ) , muscle pain ( 16 , 27% ) , nausea ( 10 , 17% ) , diarrhea ( 9 , 15% ) , vomiting ( 8 , 14% ) , runny nose ( 6 , 10% ) , and headache ( 4 , 7% ) . abdominal pain , weakness , earache , conjunctivitis , and joint stiffness were rare . twenty - five patients met the definition of ili , and 34 met the definition of p - ili ( figure ) . symptoms were more common among campers than staff ( 46.8% vs. 26.1% ; p = 0.009 ) , persons of younger age ( table 1 ) , and persons with cancer or scd ( table 2 ) . proportions were compared with 2-tailed  or fisher exact test by using epi info version 3.5 ( www.cdc.gov/epiinfo ) . outbreak curve of influenza - like illness ( ili ) and probable ili ( p - ili ) cases during the 4 days of summer camp for children with hematologic and oncologic conditions ( 14 ) and the 10 days ( 514 ) after closing the camp , louisiana , usa , 2009 . * by  test for trend for increasing age groups within each category .  p = 0.049 . * values given as no . in category / total no . with condition ( % ) . data were analyzed by using 2-tailed fisher exact test for each category compared with persons with no underlying condition . probably because of small numbers , no difference was evident in the attack rate between staff assigned and unassigned to a patrol , between boy and girl campers , between patrols , or between those who recalled or did not recall being in contact with a case - patient . twenty - six case - patients sought medical attention , and 12 ( 2 staff and 10 campers ) were hospitalized ; 8 had scd and 4 were in active cancer treatment ; all were regular - floor admissions ; none required oxygen support or other intensive care ; mean length of stay was 4.25 ( range 36 ) days ; and all recovered uneventfully . twenty - five persons ( 18 campers and 7 staff ) were tested for influenza : 13 were tested at an outside facility , of whom 3 had positive results ( method of testing unknown ) ; 12 were tested at children s hospital by rit ( binaxnow ; invernass medical , waltham , ma , usa ) and direct immunofluorescence assay ( d ultra ; diagnostic hybrids , athens , oh , usa ) , and 5 ( 42% ) had positive test results for influenza a virus . of the 5 positive specimens obtained from patients , 4 were confirmed as pandemic ( h1n1 ) 2009 virus by real - time reverse transcription  pcr . limited preliminary information is available about summer camp outbreaks of pandemic ( h1n1 ) 2009 ( 2 ) . the closest scenarios ( school outbreaks ) reported attack rates of 3%33% in the united states ( 35 ) and 2%31% in the united kingdom ( 6,7 ) . differences between studies and groups probably reflect different levels of exposure and surveillance definitions . in the outbreak reported here , the overall attack rate was 36% ; infection was more common among campers ( 47% ) , children and adolescents ( 43% ) , those with cancer ( 48% ) , and those with scd ( 82% ) . because of their underlying condition , the threshold for evaluation and intervention is lower for children with hematologic or oncologic processes , which might account for some increased reporting of symptoms , hospitalization , and extended stay . children with scd were disproportionately affected ; 82% of them reported symptoms , and 89% of those symptomatic were hospitalized because of fever or pain crisis . for seasonal influenza , the hospitalization rate is 56 higher for children with scd than those without scd ( 8) ; the same trend seems true for pandemic ( h1n1 ) 2009 infection . among those with no underlying condition , the influenza attack rate was lower ( 28% ) , few ( 11% ) persons sought medical attention , and none were hospitalized . for persons with no underlying condition , second , we used a clinical definition of ili ; however , although the limitations of the definition are well recognized , it is a well - accepted tool for outbreak investigation . fourth , only a few persons were tested to determine the causative agent . however , of the 12 patients we tested at children s hospital , 5 ( 42% ) had influenza a virus and 4 were confirmed as having pandemic ( h1n1 ) 2009 virus infection . this level of positivity is in accordance with sensitivity reported for available tests ( 9,10 ) and suggests that most , if not all , cases of ili identified were caused by pandemic ( h1n1 ) 2009 virus .
an outbreak of influenza a pandemic ( h1n1 ) 2009 occurred among campers and staff at a summer camp attended by children with hematologic and oncologic conditions . 
 the overall attack rate was 36% and was highest among children and adolescents ( 43% ) , persons with cancer ( 48% ) , and persons with sickle cell disease ( 82% ) .