the ltcf in illinois provides housing , healthcare services , and recreational activities for residents with neurologic and developmental medical conditions . during the outbreak , , the main site of the influenza outbreak , housed 108 residents in 6 wards ; 104 ( 96% ) received the 200708 influenza vaccine . of the 685 ltcf employees involved in direct patient care , 385 ( 56% ) received the 200708 influenza vaccine on site . pcr result for influenza virus from january 20 through february 8 , 2008 , in a resident of the ltcf . surveillance for new case - patients included obtaining a nasopharyngeal specimen from all residents with new onset of fever or respiratory symptoms or any unusual behavior within 24 hours after illness onset . all specimens were tested by using the quickvue a and b influenza test ( quidel , san diego , ca , usa ) . a second specimen was obtained from all persons with positive rapid test results and some ( 57% ) from persons with negative results for confirmation of influenza virus infection and virus subtyping by reverse transcription  pcr . testing for antiviral drug resistance was conducted directly on clinical specimens by pyrosequencing as described ( 6,7 ) , including identification of the oseltamivir resistance  conferring h274y mutation in the neuraminidase gene of influenza viruses ( h1n1 ) ( h275y in n1 numbering ) and the adamantane resistance  conferring mutations in the matrix 2 protein ( 7,8 ) . the ha1 portion of the hemagglutinin ( ha ) gene of the outbreak viruses was sequenced and compared with those of epidemiologically relevant viruses . phylogenetic analysis of ha1 was performed by using mega version 4.0.1 software ( 9 ) . a phylogenetic tree was inferred by using maximum composite likelihood available in mega version 4.0.1 . the outbreak investigation was considered a public health response and granted exemption from review by the institutional review board of the centers for disease control and prevention . on january 27 , the first 3 residents with fever or respiratory symptoms in ward 1 within building a were positive for influenza a virus infection by rapid test ( figure 1 ) . on january 28 , outbreak infection control measures were initiated in all 6 wards , including surveillance for new cases , 5 days of treatment with oseltamivir for confirmed cases , and 14 days of prophylaxis with oseltamivir for all healthy residents in wards with confirmed case - patients ( 2 ) . confirmed case - patients were quarantined in their rooms for 10 days ; all residents in all 6 wards were quarantined for 10 days , and visitor movement was restricted . staff and visitors were required to use personal protective equipment and practice respiratory and hand hygiene . prescriptions for prophylactic courses of oseltamivir and influenza vaccinations were offered to all staff of building a ; uptake was not recorded . number of cases of influenza by date of symptom onset and outbreak control protocol during an influenza a outbreak in a long - term care facility , illinois , usa , 2008 . retrospective medical chart review of all nontested building a residents identified 1 potential missed case - patient with influenza who had symptom onset on january 29 . additional cases were detected in 2 other residential buildings in the long - term care facility ( buildings b and c ) . building b housed 53 residents in 4 wards and building c housed 16 residents in 1 ward . all ( 100% ) of residents in both buildings had received the 200708 influenza vaccine . of the 16 rapid test specimens with negative results from all 3 buildings that were subjected to confirmatory testing , 5 ( 31% ) were positive by reverse transcription pcr for influenza a virus ( h1n1 ) . from january 28 through january 31 , 2008 , a total of 6 additional confirmed case - patients were identified . eight ( 47% ) of 17 residents in ward 1 and 1 ( 6% ) of 16 residents in ward 2 were infected with influenza a viruses ( h1n1 ) that contained the h274y mutation but did not have markers of resistance to adamantanes or zanamivir . on january 30 , high fever developed in a male resident in ward 3 while on the first day of a home visit ( figure 1 ) . he returned to building a on january 31 , was positive for influenza by rapid test , and was placed in ward 2 in an attempt to group him with other already ill residents . because of an ongoing outbreak in other nearby wards , oseltamivir prophylaxis was initiated for all residents in ward 3 who were not ill . on february 1 , symptoms developed in 2 other residents in ward 3 who were positive for influenza by rapid test . three ( 18% ) confirmed cases of influenza a virus ( h3n2 ) resistant to adamantanes but sensitive to oseltamivir were detected among 17 residents in ward 3 . additional cases , but no clusters , were detected in other buildings 12 weeks later . characteristics of case - patients are shown in the table . establishing a firm epidemiologic link between cases , antiviral drug resistance results became available on february 7 when all case - patients had completed their treatment courses . ongoing prophylaxis courses were changed : oseltamivir was replaced with rimantadine in ward 1 , and rimantadine was added to oseltamivir in ward 2 . one case - patient was hospitalized for parotitis to rule out infection with mumps and was discharged in stable condition after 1 day . one case - patient who had a diagnosis of end - stage lung disease and a do not resuscitate / do not intubate directive died . sequence analysis of the ha1 gene in outbreak influenza a viruses ( h1n1 ) showed identical or nearly identical sequences , differing by only 1 or 2 nt ( figure 2 ) . these viruses were phylogenetically more closely related to a / brisbane/59/2007 ( h1n1 ) than to the a / solomon islands/3/2006 , the influenza a virus ( h1n1 ) strain in the 200708 influenza vaccine . genbank accession numbers of ha ( ha1 ) sequences for the 9 oseltamivir - resistant influenza a viruses ( h1n1 ) are fj231752fj231760 . phylogenetic analysis of the hemagglutinin gene ( ha1 portion ) of influenza a viruses ( h1n1 ) isolated during an influenza a outbreak in a long - term care facility , illinois , usa , 2008 . one of the viruses from building b was more similar in sequence to 1 virus from building a. however , this finding could reflect natural variance in circulating viruses . red indicates outbreak viruses , boldface italics indicates vaccine strain for 200809 , boldface indicates vaccine strain for 200708 , and arrows indicate nucleotide differences in ha1 subunit . the attack rate of illness caused by oseltamivir - resistant influenza a viruses ( h1n1 ) in ward 1 was within the range ( 20%80% ) reported for other facility influenza outbreaks ( 1,10,11 ) , indicating effective person - to - person transmission of oseltamivir - resistant influenza a viruses ( h1n1 ) . nosocomial transmission of oseltamivir - resistant influenza a viruses ( h1n1 ) , with possible healthcare worker involvement , has been described ( 12 ) . before the 200708 influenza season , transmission of neuraminidase - resistant influenza viruses had rarely been reported ( 13 ) . although we documented a relatively high attack rate in 1 ward ( ward 1 ) , and despite resistance to the antiviral agent initially used , the outbreak abated quickly . high annual vaccination rates among residents and relatively high rates among employees ( 2 ) may have played a role in limiting the spread of the outbreak viruses . however , the a / brisbane/59/2007 ( h1n1)like outbreak viruses were not optimally matched to the a / solomon islands/3/2006 ( h1n1 ) vaccine strain ( 14 ) . also , infection control measures , such as isolation and quarantine , likely played a role in controlling this outbreak . the proportion of circulating influenza viruses resistant to oseltamivir increased from 12% during the 200708 season to 99% during the 200809 season in the united states , and new interim guidelines for use of antiviral agents were released in december 2008 ( 15 ) . these guidelines were updated for the 200910 season to account for the emergence of pandemic ( h1n1 ) 2009 virus in september 2009 ( www.cdc.gov/h1n1flu/recommendations.htm ) . this outbreak underscores the possibility of 2 influenza a viruses , with different antiviral susceptibilities , in the same facility . during a facility outbreak of influenza , providers should consult antiviral recommendations of the centers for disease control and prevention and obtain influenza virus typing and subtyping to guide appropriate antiviral drug choices .
an outbreak of oseltamivir - resistant influenza a ( h1n1 ) occurred in a long - term care facility . 
 eight ( 47% ) of 17 and 1 ( 6% ) of 16 residents in 2 wards had oseltamivir - resistant influenza a virus ( h1n1 ) infections . 
 initial outbreak response included treatment and prophylaxis with oseltamivir . 
 the outbreak abated , likely because of infection control measures .