from october to november 2002 , a cluster of skin and soft tissue infections due to mrsa involving pediatric and maternity patients occurred at a new york city hospital .
the hospital has a labor and delivery unit and 2 units that house both healthy newborns and maternity patients .
after the outbreak was recognized , the following interventions were implemented : 1 ) nursing and medical personnel from the involved areas were informed of the outbreak and potential modes of transmission of staphylococci , 2 ) contact precautions were emphasized for all patients with suspected or proven skin infections , 3 ) alcohol - based hand sanitizers were placed in involved areas , 4 ) healthcare workers from involved units were screened for nasal mrsa colonization , and 5 ) environmental surfaces ( including cord clamps , antitheft transponders , and temperature sensors of baby warmers ) were tested for mrsa contamination .
healthcare workers colonized with mrsa were treated with intranasal mupirocin and furloughed until repeat cultures were negative . to identify any other potential case - patients , letters concerning the outbreak
were sent to pediatricians who cared for newborns discharged from the affected units during the outbreak period .
cases were defined as mrsa infections in patients who stayed on the labor and delivery , nursery , or maternity units at any time from october 2002 to december 2002 .
the medical records of the patients were reviewed for information regarding prior healthcare exposures , receipt of antimicrobial agents , underlying medical conditions , treatment , and clinical outcome .
cultures related to the outbreak were grown on tryptic soy agar plates supplemented with 3% sheep blood ; colonies consistent with s. aureus were identified according to standard techniques .
all isolates underwent susceptibility testing with the etest method ( ab biodisk , solna , sweden ) .
ribotyping was performed with the riboprinter microbial characterization system ( qualicon , wilmington , de , usa ) , as previously noted ( 13 ) .
in addition , isolates of mrsa collected during the outbreak were fingerprinted by pulsed - field gel electrophoresis ( pfge ) , as previously described ( 13 ) .
sccmec typing was performed by using multiplex polymerase chain reaction ( pcr ) , under conditions described by oliveira et al .
primers to detect the meca gene were included as an internal positive control ( 15 ) .
multilocus sequence typing ( mlst ) was performed on selected isolates as described by enright et al .
bidirectional dna sequencing of 7 amplified housekeeping genes was performed with an automated fluorescent dye - terminator sequencing system ( applied biosystems , foster city , ca , usa ) .
the presence of genetic sequences encoding several staphylococcal toxins was also investigated for the outbreak isolates .
based on the previously reported distribution of enterotoxins in ca - mrsa from the united states ( 7 ) , the following toxins were selected for investigation : staphylococcal enterotoxin a ( sea ) , b ( seb ) , c ( sec ) , h ( seh ) , and k ( sek ) . in addition , strains were screened for pvl and toxic shock syndrome toxin-1 ( tsst-1 ) .
previously published primers and conditions were used to detect sequences encoding for sea , seb , sec , seh , pvl , and tsst-1 ( 1719 ) .
genes encoding for sek were detected with the following primers : sek forward : 5-tggatcaatggaaatcacaaaa-3  and reverse : 5-tttggtagcccatcatctcc-3  ( predicted product size 287 bp ) .
the identification of mw2 in the outbreak of the neonatal - maternity unit prompted a retrospective investigation to determine the regional prevalence of mrsa resembling this strain . in 1999 , 2001 , and 2003 , surveillance studies were performed in brooklyn , new york .
each surveillance study involved collecting all single - patient isolates of s. aureus from clinical microbiology laboratories during a 3-month interval .
susceptibility testing was performed in the central research laboratory by using the agar dilution method according to nccls methodology ( 20 ) .
all mrsa isolates were then screened for a phenotype of susceptibility to clindamycin and ciprofloxacin ( typical for mw2 ) .
the study was approved by the institutional review board at the state university of new york ( suny ) health science center and maimonides medical center .
from october to november 2002 , a cluster of skin and soft tissue infections due to mrsa involving pediatric and maternity patients occurred at a new york city hospital .
the hospital has a labor and delivery unit and 2 units that house both healthy newborns and maternity patients .
after the outbreak was recognized , the following interventions were implemented : 1 ) nursing and medical personnel from the involved areas were informed of the outbreak and potential modes of transmission of staphylococci , 2 ) contact precautions were emphasized for all patients with suspected or proven skin infections , 3 ) alcohol - based hand sanitizers were placed in involved areas , 4 ) healthcare workers from involved units were screened for nasal mrsa colonization , and 5 ) environmental surfaces ( including cord clamps , antitheft transponders , and temperature sensors of baby warmers ) were tested for mrsa contamination .
healthcare workers colonized with mrsa were treated with intranasal mupirocin and furloughed until repeat cultures were negative . to identify any other potential case - patients , letters concerning the outbreak
were sent to pediatricians who cared for newborns discharged from the affected units during the outbreak period .
cases were defined as mrsa infections in patients who stayed on the labor and delivery , nursery , or maternity units at any time from october 2002 to december 2002 .
the medical records of the patients were reviewed for information regarding prior healthcare exposures , receipt of antimicrobial agents , underlying medical conditions , treatment , and clinical outcome .
cultures related to the outbreak were grown on tryptic soy agar plates supplemented with 3% sheep blood ; colonies consistent with s. aureus were identified according to standard techniques .
all isolates underwent susceptibility testing with the etest method ( ab biodisk , solna , sweden ) .
ribotyping was performed with the riboprinter microbial characterization system ( qualicon , wilmington , de , usa ) , as previously noted ( 13 ) .
in addition , isolates of mrsa collected during the outbreak were fingerprinted by pulsed - field gel electrophoresis ( pfge ) , as previously described ( 13 ) .
sccmec typing was performed by using multiplex polymerase chain reaction ( pcr ) , under conditions described by oliveira et al .
primers to detect the meca gene were included as an internal positive control ( 15 ) .
multilocus sequence typing ( mlst ) was performed on selected isolates as described by enright et al .
bidirectional dna sequencing of 7 amplified housekeeping genes was performed with an automated fluorescent dye - terminator sequencing system ( applied biosystems , foster city , ca , usa ) .
the presence of genetic sequences encoding several staphylococcal toxins was also investigated for the outbreak isolates .
based on the previously reported distribution of enterotoxins in ca - mrsa from the united states ( 7 ) , the following toxins were selected for investigation : staphylococcal enterotoxin a ( sea ) , b ( seb ) , c ( sec ) , h ( seh ) , and k ( sek ) . in addition , strains were screened for pvl and toxic shock syndrome toxin-1 ( tsst-1 ) .
previously published primers and conditions were used to detect sequences encoding for sea , seb , sec , seh , pvl , and tsst-1 ( 1719 ) .
genes encoding for sek were detected with the following primers : sek forward : 5-tggatcaatggaaatcacaaaa-3  and reverse : 5-tttggtagcccatcatctcc-3  ( predicted product size 287 bp ) .
the identification of mw2 in the outbreak of the neonatal - maternity unit prompted a retrospective investigation to determine the regional prevalence of mrsa resembling this strain . in 1999 , 2001 , and 2003 , surveillance studies were performed in brooklyn , new york .
each surveillance study involved collecting all single - patient isolates of s. aureus from clinical microbiology laboratories during a 3-month interval .
susceptibility testing was performed in the central research laboratory by using the agar dilution method according to nccls methodology ( 20 ) .
all mrsa isolates were then screened for a phenotype of susceptibility to clindamycin and ciprofloxacin ( typical for mw2 ) .
the study was approved by the institutional review board at the state university of new york ( suny ) health science center and maimonides medical center .
from october 18 to november 28 , 2002 , a total of 8 patients with skin and soft tissue infections due to mrsa were identified . during this period
, 3.5 cases of mrsa infection occurred each month in the nursery and maternity units .
in contrast , no mrsa infections had been reported from the involved units in the 10 months before the outbreak .
two patients were mothers , and 6 were neonates ; in no instance were both the mother and her child infected .
all had been hospitalized on an involved unit at some point from october 16 to november 6 , 2002 .
review of medical records showed that none of the patients had prior hospital exposure , underlying chronic medical conditions , or recent antibiotic therapy .
patients stayed on the unit for an average of 5 days ( range 212 days ) .
clinical infection developed in 4 of the newborns and 1 mother while in the hospital .
symptoms developed in 2 newborns and 1 mother 2 , 10 , and 24 days , respectively , after discharge .
definitive therapy generally consisted of topical or systemic antimicrobial agents active against mrsa ; 1 patient required surgical drainage .
time course of hospitalizations and onset of methicillin - resistant stpahylococcus aureus illness during the outbreak at hospital a. solid bars represent period of hospitalization ; arrows represent onset of clinical infection .
the first was in an infant , born in november 2002 , who was seen as an outpatient for pustulosis ; however , the site was not cultured .
the second case involved another infant , also born in november 2002 , who was readmitted to the hospital 4 days later for treatment of omphalitis .
no additional cases were reported from december10 , 2002 , to december 31 , 2003 .
susceptibility testing showed that all 8 isolates were susceptible to clindamycin , ciprofloxacin , trimethoprim - sulfamethoxazole , rifampin , doxycycline , linezolid , and vancomycin .
of the 8 clinical isolates , 7 ( isolates p1-p7 ) belonged to 1 ribotype that was identical to the prototypical mw2 strain ( figure 2 ) .
pfge confirmed that the 7 isolates were identical and closely related to mw2 ( figure 2 ) .
since the 7 isolates appeared identical , mlst was performed on one of the isolates and showed sequence type 1 .
the pfge and mlst pattern are the same as ca - mrsa clone usa 400 , which also includes mw2 ( 21 ) . among these 7 isolates ,
all contained sek and pvl , 6 contained sec and seh , and 5 contained sea .
the eighth clinical isolate , from a catheter - site infection , was distinct from the outbreak strain by ribotyping and pfge ( figure 2 ) .
for this isolate , sccmec was nontypable , and mlst typing confirmed a distinct allelic profile .
a ) ribotype and b ) pulsed - field gel electrophoresis patterns of 8 clinical isolates of methicillin - resistant staphylococcus aureus .
clinical isolate p8 and the 3 isolates from healthcare workers ( s1s3 ) are unrelated to the outbreak strain .
a total of 189 healthcare workers worked on the involved units during the outbreak period .
screening cultures of the anterior nares were performed in 176 of the workers in november 2002 .
three of the cultures were positive for mrsa , including 2 from the nursing staff and 1 from a pediatrician .
the 3 mrsa strains possessed a susceptibility pattern typical for the multidrug - resistant hospital strains , with resistance to clindamycin and ciprofloxacin .
they belonged to ribotypes distinct from the outbreak clone , and pfge confirmed these isolates were unrelated to mw2 ( figure 2 ) .
none of the 27 environmental samples collected in november 2002 yielded positive cultures for mrsa .
a total of 4,345 isolates of s. aureus were collected in the 3 surveillance studies conducted in 1999 , 2001 , and 2003 ; susceptibility data for these isolates are given in table 2 .
the 1,913 mrsa isolates , 118 ( 6% ) possessed the screened phenotype ( susceptible to both clindamycin and fluoroquinolones ) . among the 118 isolates ,
a total of 11 isolates possessed the same ribotype pattern as the outbreak clone , mw2 .
sources of the cultures included skin and soft - tissue in 7 patients , blood / sterile body fluid in 3 patients , and the genital tract in 1 patient .
the number of isolates resembling mw2 remained relatively constant during the 3 surveillances ( 4 in 1999 , 3 in 2001 , and 4 in 2003 ) .
from october 18 to november 28 , 2002 , a total of 8 patients with skin and soft tissue infections due to mrsa were identified . during this period
, 3.5 cases of mrsa infection occurred each month in the nursery and maternity units .
in contrast , no mrsa infections had been reported from the involved units in the 10 months before the outbreak .
two patients were mothers , and 6 were neonates ; in no instance were both the mother and her child infected .
all had been hospitalized on an involved unit at some point from october 16 to november 6 , 2002 .
review of medical records showed that none of the patients had prior hospital exposure , underlying chronic medical conditions , or recent antibiotic therapy .
patients stayed on the unit for an average of 5 days ( range 212 days ) .
clinical infection developed in 4 of the newborns and 1 mother while in the hospital .
symptoms developed in 2 newborns and 1 mother 2 , 10 , and 24 days , respectively , after discharge .
definitive therapy generally consisted of topical or systemic antimicrobial agents active against mrsa ; 1 patient required surgical drainage .
time course of hospitalizations and onset of methicillin - resistant stpahylococcus aureus illness during the outbreak at hospital a. solid bars represent period of hospitalization ; arrows represent onset of clinical infection .
the first was in an infant , born in november 2002 , who was seen as an outpatient for pustulosis ; however , the site was not cultured .
the second case involved another infant , also born in november 2002 , who was readmitted to the hospital 4 days later for treatment of omphalitis .
no additional cases were reported from december10 , 2002 , to december 31 , 2003 .
susceptibility testing showed that all 8 isolates were susceptible to clindamycin , ciprofloxacin , trimethoprim - sulfamethoxazole , rifampin , doxycycline , linezolid , and vancomycin .
of the 8 clinical isolates , 7 ( isolates p1-p7 ) belonged to 1 ribotype that was identical to the prototypical mw2 strain ( figure 2 ) .
pfge confirmed that the 7 isolates were identical and closely related to mw2 ( figure 2 ) .
since the 7 isolates appeared identical , mlst was performed on one of the isolates and showed sequence type 1 .
the pfge and mlst pattern are the same as ca - mrsa clone usa 400 , which also includes mw2 ( 21 ) . among these 7 isolates ,
all contained sek and pvl , 6 contained sec and seh , and 5 contained sea .
the eighth clinical isolate , from a catheter - site infection , was distinct from the outbreak strain by ribotyping and pfge ( figure 2 ) .
for this isolate , sccmec was nontypable , and mlst typing confirmed a distinct allelic profile .
a ) ribotype and b ) pulsed - field gel electrophoresis patterns of 8 clinical isolates of methicillin - resistant staphylococcus aureus .
clinical isolate p8 and the 3 isolates from healthcare workers ( s1s3 ) are unrelated to the outbreak strain .
a total of 189 healthcare workers worked on the involved units during the outbreak period .
screening cultures of the anterior nares were performed in 176 of the workers in november 2002 .
three of the cultures were positive for mrsa , including 2 from the nursing staff and 1 from a pediatrician .
the 3 mrsa strains possessed a susceptibility pattern typical for the multidrug - resistant hospital strains , with resistance to clindamycin and ciprofloxacin .
they belonged to ribotypes distinct from the outbreak clone , and pfge confirmed these isolates were unrelated to mw2 ( figure 2 ) .
none of the 27 environmental samples collected in november 2002 yielded positive cultures for mrsa .
a total of 4,345 isolates of s. aureus were collected in the 3 surveillance studies conducted in 1999 , 2001 , and 2003 ; susceptibility data for these isolates are given in table 2 .
the 1,913 mrsa isolates , 118 ( 6% ) possessed the screened phenotype ( susceptible to both clindamycin and fluoroquinolones ) . among the 118 isolates ,
a total of 11 isolates possessed the same ribotype pattern as the outbreak clone , mw2 .
sources of the cultures included skin and soft - tissue in 7 patients , blood / sterile body fluid in 3 patients , and the genital tract in 1 patient .
the number of isolates resembling mw2 remained relatively constant during the 3 surveillances ( 4 in 1999 , 3 in 2001 , and 4 in 2003 ) .
this report characterizes the nosocomial transmission of the ca - mrsa strain mw2 among healthy newborns and , possibly , a postpartum woman .
symptoms developed in 3 patients 224 days after hospitalization ; 2 may have acquired the bacteria in the hospital or the community . an eighth patient , a mother with catheter - site infection , had an unrelated strain with a pattern suggestive of a hospital - associated strain .
the source of the outbreak and mechanism of transmission were not evident , as no cultures of staff members or the environment yielded this particular strain of mrsa .
transmission may have occurred after mw2 was introduced into the hospital by transient colonization of healthcare workers or by contamination of shared medical equipment .
the infection control measures enacted in response to the initial cases may have had a role in controlling the outbreak .
widespread screening of healthcare workers for mrsa did not detect the outbreak strain in this and another report ( 12 ) .
while a potential role for this practice can not be excluded , current evidence does not support routinely implementing widespread screening for ca - mrsa . in the pediatric population ,
risk factors associated with mrsa infections include premature birth or low birth weight , chronic underlying diseases , prolonged hospitalization , invasive or surgical procedures , indwelling catheters , and prolonged use of antimicrobial agents ( 2225 ) .
prior outbreaks involving the pandemic strain phage type 80/81 were characterized by high colonization rates among infants discharged from nurseries and subsequent transmission to family members ( 26 ) . in this report , infection developed in the outpatient setting for 2 patients ( following an admission on the involved unit ) , which suggests carriage of mw2 from the hospital back into the community .
unrecognized ca - mrsa colonization during hospitalization could become an additional method of its dissemination in the community .
increased prevalence of ca - mrsa has been reported in chicago , los angeles , texas , and minnesota ( 2,3,27,28 ) . in new york city
, ca - mrsa appears less common ; 1 investigation reported mrsa carriage in 0.26% of children and their guardians ( 29 ) . in our present report
, a retrospective analysis of isolates collected from citywide surveillance studies conducted from 1999 to 2003 suggests that 1% of all mrsa isolates in brooklyn are genotypically related to the prototypical north american ca - mrsa , mw2 .
since only mrsa isolates that were susceptible to both clindamycin and ciprofloxacin were analyzed , this analysis probably underestimates the true prevalence .
other strains of ca - mrsa ( e.g. , usa 300 ) and usa 400 strains that acquired resistance to these antimicrobial agents would have been missed by our screening methods .
the introduction of ca - mrsa strains into neonatal units represents an especially serious challenge .
many of the infections caused by these strains , including some in our report , can be unusually severe and life - threatening ( 11 ) .
careful vigilance involving surveillance , identification of these dangerous strains , and implementation of infection control measures , should be helpful in preventing further transmission both within and outside of the hospital .
 community - associated methicillin - resistant staphylococcus aureus ( ca - mrsa ) has rarely been reported in the hospital setting . 
 we report an outbreak of 7 cases of skin and soft tissue infections due to a strain of ca - mrsa . 
 all patients were admitted to the labor and delivery , nursery , or maternity units during a 3-week period . 
 genetic fingerprinting showed that the outbreak strain was closely related to the usa 400 strain that includes the midwestern strain mw2 . 
 all isolates contained the staphylococcal chromosome cassette mec type iv . 
 genes for panton - valentine leukocidin and staphylococcal enterotoxin k were detected in all isolates , and most contained other enterotoxin genes . 
 testing of nearly 2,000 mrsa isolates collected during citywide surveillance studies from 1999 to 2003 showed that 1% were genetically related to mw2 . 
 ca - mrsa strain mw2 has been present in this region at least since 1999 . 
 this study documents the spread of this strain among healthy newborns at 1 hospital . 
Materials and Methods
Outbreak Investigation at Hospital A
Surveillance Study
Results
Outbreak Investigation at Hospital A
Surveillance Study
Discussion