title: Hospital-acquired listeriosis outbreak caused by contaminated diced celery--Texas, 2010.
abstract: BACKGROUND
  Listeria monocytogenes causes often-fatal infections affecting mainly immunocompromised persons. Sources of hospital-acquired listeriosis outbreaks can be difficult to identify. We investigated a listeriosis outbreak spanning 7 months and involving 5 hospitals.
  
  
  METHODS
  Outbreak-related cases were identified by pulsed-field gel electrophoresis (PFGE) and confirmed by multiple-locus variable-number tandem-repeat analysis (MLVA). We conducted patient interviews, medical records reviews, and hospital food source evaluations. Food and environmental specimens were collected at a hospital (hospital A) where 6 patients had been admitted before listeriosis onset; these specimens were tested by culture, polymerase chain reaction (PCR), and PFGE. We collected and tested food and environmental samples at the implicated processing facility.
  
  
  RESULTS
  Ten outbreak-related patients were immunocompromised by ≥1 underlying conditions or treatments; 5 died. All patients had been admitted to or visited an acute-care hospital during their possible incubation periods. The outbreak strain of L. monocytogenes was isolated from chicken salad and its diced celery ingredient at hospital A, and in 19 of >200 swabs of multiple surfaces and in 8 of 11 diced celery products at the processing plant. PCR testing detected Listeria in only 3 of 10 environmental and food samples from which it was isolated by culturing. The facility was closed, products were recalled, and the outbreak ended.
  
  
  CONCLUSIONS
  Contaminated diced celery caused a baffling, lengthy outbreak of hospital-acquired listeriosis. PCR testing often failed to detect the pathogen, suggesting its reliability should be further evaluated. Listeriosis risk should be considered in fresh produce selections for immunocompromised patients.
authors.affiliation: Emerging and Acute Infectious Diseases Branch, Texas Department of State Health Services, 1100 W 49th St, Austin, TX 78756, USA. linda.gaul@dshs.state.tx.us
authors.forename: Linda Knudson
authors.initials: LK
authors.lastname: Gaul
authors.forename: Noha H
authors.initials: NH
authors.lastname: Farag
authors.forename: Trudi
authors.initials: T
authors.lastname: Shim
authors.forename: Monica A
authors.initials: MA
authors.lastname: Kingsley
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Silk
authors.forename: Eija
authors.initials: E
authors.lastname: Hyytia-Trees
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000077102:Apium / Q000382:microbiology*; D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D016521:Electrophoresis, Gel, Pulsed-Field; D005260:Female; D005516:Food Microbiology; D005521:Food Service, Hospital; D005517:Foodborne Diseases / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D055256:Infectious Disease Incubation Period; D008089:Listeria monocytogenes / Q000302:isolation & purification*; D008088:Listeriosis / Q000453:epidemiology* / Q000382:microbiology; D008297:Male; D008875:Middle Aged; D013781:Texas / Q000453:epidemiology