Pertussis pseudo-outbreak linked to specimens contaminated by Bordetella pertussis DNA from clinic surfaces

Sema Mandal*, Kathleen M. Tatti, Denise Woods-Stout, Pamela K. Cassiday, Amanda E. Faulkner, Matthew M. Griffith, Michael L. Jackson, Lucia C. Pawloski, Bari Wagner, Meghan Barnes, Amanda C. Cohn, Ken A. Gershman, Nancy E. Messonnier, Thomas A. Clark, Maria Lucia C. Tondella, Stacey W. Martin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

39 Citations (Scopus)


BACKGROUND AND OBJECTIVES: We investigated a pertussis outbreak characterized by atypical cases, confirmed by polymerase chain reaction (PCR) alone at a single laboratory, which persisted despite high vaccine coverage and routine control measures. We aimed to determine whether Bordetella pertussis was the causative agent and advise on control interventions. METHODS: We conducted case ascertainment, confirmatory testing for pertussis and other pathogens, and an assessment for possible sources of specimen contamination, including a survey of clinic practices, sampling clinics for B pertussis DNA, and review of laboratory quality indicators. RESULTS: Between November 28, 2008, and September 4, 2009, 125 cases were reported, of which 92 (74%) were PCR positive. Cases occurring after April 2009 (n = 79; 63%) had fewer classic pertussis symptoms (63% vs 98%; P < .01), smaller amounts of B pertussis DNA (mean PCR cycle threshold value: 40.9 vs 33.1; P < .01), and a greater proportion of PCR-positive results (34% vs 6%; P < .01). Cultures and serology for B pertussis were negative. Other common respiratory pathogens were detected. We identified factors that likely resulted in specimen contamination at the point of collection: environmentally present B pertussis DNA in clinics from vaccine, clinic standard specimen collection practices, use of liquid transport medium, and lack of clinically relevant PCR cutoffs. CONCLUSIONS: A summer pertussis pseudo-outbreak, multifactorial in cause, likely occurred. Recommendations beyond standard practice were made to providers on specimen collection and environmental cleaning, and to laboratories on standardizing PCR protocols and reporting results, to minimize false-positive results from contaminated clinical specimens.

Original languageEnglish
Pages (from-to)e424-e430
Issue number2
Publication statusPublished - Feb 2012
Externally publishedYes


  • Bordetella pertussis
  • Cross contamination
  • Diagnostic errors
  • Disease outbreak
  • False positive result
  • Polymerase chain reaction


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