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Successful control of a norovirus outbreak among attendees of a hospital teaching conference
American Journal of Infection Control 40 (2012) 73-4
Contents lists available at ScienceDirect
American Journal of Infection Control
American Journal of Infection Control
journal homepage: www.ajicjournal.org
Brief report
Successful control of a norovirus outbreak among attendees of a hospital teaching conference Christopher Vinnard MD, MPH, MSCE a, *, Ingi Lee MD, MSCE a, Darren Linkin MD, MSCE a, b a b
Department of Medicine, Division of Infectious Diseases, University of Pennsylvania School of Medicine, Philadelphia, PA Philadelphia Veterans Affairs Medical Center, Philadelphia, PA
Key Words: Infection control Health care Gastroenteritis
We report an outbreak of norovirus gastroenteritis after a hospital teaching conference, and describe the specific measures instituted by the infection control team. No secondary cases of norovirus infection were identified among hospital staff or patients. In a case-control study, we identified multiple food source contamination as the source of the outbreak. Our report highlights the potential success of a multifaceted infection control strategy in preventing the transmission of norovirus in health care settings. Copyright Ó 2012 by the Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.
Norovirus is the most common cause of foodborne illness in the United States.1 The probability of infection for a single norovirus virion is higher than any other viral virion causing clinical gastroenteritis, with an infectious dose of only several hundred viral particles.2 Norovirus is typically transmitted person to person, and the risk for airborne transmission is inversely associated with distance from the vomiting index patient.3 However, norovirus can also spread via contaminated food, water, and surfaces.4 Previous reports of norovirus outbreaks in health care settings have highlighted the potential for transmission between patients.5 Less is known about the effectiveness of measures aimed at preventing norovirus transmission from infected staff to uninfected staff and patients. We report our investigation and control of a norovirus gastroenteritis outbreak among employees at a VA Medical Center, describe the infection control efforts that prevented the development of secondary cases, and present the results of a case-control study that identified the outbreak source.
a local caterer provided lunch. During the 2 days after the conference, the department noted a significant number of employees calling in sick with gastrointestinal complaints, and the infection control team was contacted to investigate and manage a suspected outbreak of foodborne illness among conference attendees. Our initial investigation found that most subjects had onset of symptoms (primarily vomiting) within 24 hours after the conference. After questioning supervisors and clinicians, we did not find any similar cases among other employee groups or inpatients. We surveyed all employees who had attended the conference about the nature and timing of symptoms and the specific food items that were eaten at the conference. Based on the high prevalence of vomiting among symptomatic employees, we defined cases as individuals who developed vomiting after attending the conference and controls as individuals who attended the conference but denied subsequent vomiting or diarrhea. We calculated the odds of symptomatic illness associated with the consumption of individual food items at the conference.
METHODS The Department of Behavioral Health at the Philadelphia VA Medical Center held its weekly grand rounds conference, at which
RESULTS
* Address correspondence to Christopher Vinnard, MD, MPH, MSCE, Division of Infectious Diseases, University of Pennsylvania School of Medicine, 502 Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104. E-mail address: [email protected] (C. Vinnard). A portion of this work was presented as an abstract at the Annual Scientific Meeting of the Society for Healthcare Epidemiology of America, March 2011. C.V. received salary support through a National Institutes of Health Institutional Research Training Grant (T32). Conflicts of interest: None to report.
We obtained 63 surveys from conference attendees, including 23 individuals who reported vomiting and 35 individuals who reported no symptoms. Five individuals reported symptoms that did not include vomiting and were excluded from the analysis. Two symptomatic employees with diarrhea presented to Occupational Health, and both had stool specimens that were positive for norovirus by nucleic acid testing and negative for all bacterial pathogens tested.
0196-6553/$36.00 - Copyright Ó 2012 by the Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.ajic.2011.03.033
74
C. Vinnard et al. / American Journal of Infection Control 40 (2012) 73-4
Table 1 Odds of symptomatic illness associated with specific food items
Food item Ham sandwich Ice Potato chips Turkey sandwich Chocolate chip cookies
Cases (N ¼ 23), n (%) 12 12 15 8 12
(52) (52) (65) (35) (52)
Controls (N ¼ 35), n (%) 2 5 8 5 11
(6) (14) (23) (14) (31)
OR (95% CI) 18.0 6.5 6.3 3.2 2.4
(3.1-179.0) (1.6-28.6) (1.7-24.0) (0.8-14.5)* (0.7-8.1)*
*Not significant (P > .05).
The individual food items with a significant odds ratio (OR) for illness included ham sandwich (OR, 18; 95% confidence interval [CI], 3-179), ice (OR, 7; 95% CI, 2-29), and potato chips (OR, 6; 95% CI, 2-24) (Table 1). Both the ice and the chips came from shared open containers. Seven individuals attended the conference but did not eat, and none of these individuals developed symptoms. After our investigation, the city Health Department was notified, and the caterer was evaluated. The Health Department informed us that there were no significant health code violations, but could not report to us whether there were any ill employees. We initiated several infection control measures. Hand hygiene was reinforced among all employees. A phenolic cleaning agent (Ready-To-Use Wex-Cide; Wexford Labs, Kirkwood, MO) was used to clean the room in which the grand rounds conference was held, at concentrations viricidal against norovirus. All symptomatic employees were sent home, and were instructed to remain at home until 72 hours after symptoms resolved. Daily reviews with supervisors and clinicians were conducted after notification of the infection control team, and no secondary cases of norovirus gastroenteritis were identified among either hospital employees or patients. DISCUSSION A recent meta-analysis found no evidence that infection control interventions shortened the duration of norovirus outbreaks (22 days when infection control measures were implemented vs 18 days without specific measures).6 Several factors likely contributed to the success of our efforts in containing this outbreak of norovirus gastroenteritis. First, the infection control team was notified within 1 day of the first report of symptoms, and previous work has shown that timely identification of nosocomial transmission is essential for containing a norovirus outbreak.5 Rapid
decontamination of the outbreak site with terminal cleaning agents is also critical, given the central role of environmental surface contamination in the propagation of norovirus outbreaks.7 In addition, all sick employees were instructed to remain at home until asymptomatic for 72 hours, limiting contact of infected employees with uninfected employees and patients during the period of greatest infectivity. Finally, the outbreak was associated with a conference setting rather than a patient care location (although many of the conference attendees had clinical responsibilities). Both presymptomatic and postsymptomatic individuals have been implicated as sources of norovirus outbreaks, and norovirus shedding among asymptomatic food handlers has been documented.8 Based on the multiple food sources identified in the casecontrol study, we suspect that contamination with norovirus occurred either at the site of preparation by a food handler or during the distribution of food before the conference. One limitation of our study is that we were unable to determine whether ill employees had been involved at any stage of food preparation or delivery. In summary, our investigation highlights the potential for multiple food source contamination with norovirus, and demonstrates the success that a multifaceted infection control strategy can have in preventing the transmission of norovirus from infected hospital staff to uninfected hospital staff and patients.
References 1. Scallan E, Hoekstra RM, Angulo FJ, Tauxe RV, Widdowson MA, Roy SL, et al. Foodborne illness acquired in the United States: major pathogens. Emerg Infect Dis 2011;17:7-15. 2. Teunis PF, Moe CL, Liu P, Miller SE, Lindesmith L, Baric RS, et al. Norwalk virus: how infectious is it? J Med Virol 2008;80:1468-76. 3. Marks PJ, Vipond IB, Carlisle D, Deakin D, Fey RE, Caul EO. Evidence for airborne transmission of Norwalk-like virus (NLV) in a hotel restaurant. Epidemiol Infect 2000;124:481-7. 4. Glass RI, Parashar UD, Estes MK. Norovirus gastroenteritis. N Engl J Med 2009; 361:1776-85. 5. Johnston CP, Qiu H, Ticehurst JR, Dickson C, Rosenbaum P, Lawson P, et al. Outbreak management and implications of a nosocomial norovirus outbreak. Clin Infect Dis 2007;45:534-40. 6. Harris JP, Lopman BA, O’Brien SJ. Infection control measures for norovirus: a systematic review of outbreaks in semi-enclosed settings. J Hosp Infect 2010; 74:1-9. 7. Wu HM, Fornek M, Schwab KJ, Chapin AR, Gibson K, Schwab E, et al. A norovirus outbreak at a long-term-care facility: the role of environmental surface contamination. Infect Control Hosp Epidemiol 2005;26:802-10. 8. Okabayashi T, Yokota S, Ohkoshi Y, Ohuchi H, Yoshida Y, Kikuchi M, et al. Occurrence of norovirus infections unrelated to norovirus outbreaks in an asymptomatic food handler population. J Clin Microbiol 2008;46:1985-8.
Contents lists available at ScienceDirect
American Journal of Infection Control
American Journal of Infection Control
journal homepage: www.ajicjournal.org
Brief report
Successful control of a norovirus outbreak among attendees of a hospital teaching conference Christopher Vinnard MD, MPH, MSCE a, *, Ingi Lee MD, MSCE a, Darren Linkin MD, MSCE a, b a b
Department of Medicine, Division of Infectious Diseases, University of Pennsylvania School of Medicine, Philadelphia, PA Philadelphia Veterans Affairs Medical Center, Philadelphia, PA
Key Words: Infection control Health care Gastroenteritis
We report an outbreak of norovirus gastroenteritis after a hospital teaching conference, and describe the specific measures instituted by the infection control team. No secondary cases of norovirus infection were identified among hospital staff or patients. In a case-control study, we identified multiple food source contamination as the source of the outbreak. Our report highlights the potential success of a multifaceted infection control strategy in preventing the transmission of norovirus in health care settings. Copyright Ó 2012 by the Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.
Norovirus is the most common cause of foodborne illness in the United States.1 The probability of infection for a single norovirus virion is higher than any other viral virion causing clinical gastroenteritis, with an infectious dose of only several hundred viral particles.2 Norovirus is typically transmitted person to person, and the risk for airborne transmission is inversely associated with distance from the vomiting index patient.3 However, norovirus can also spread via contaminated food, water, and surfaces.4 Previous reports of norovirus outbreaks in health care settings have highlighted the potential for transmission between patients.5 Less is known about the effectiveness of measures aimed at preventing norovirus transmission from infected staff to uninfected staff and patients. We report our investigation and control of a norovirus gastroenteritis outbreak among employees at a VA Medical Center, describe the infection control efforts that prevented the development of secondary cases, and present the results of a case-control study that identified the outbreak source.
a local caterer provided lunch. During the 2 days after the conference, the department noted a significant number of employees calling in sick with gastrointestinal complaints, and the infection control team was contacted to investigate and manage a suspected outbreak of foodborne illness among conference attendees. Our initial investigation found that most subjects had onset of symptoms (primarily vomiting) within 24 hours after the conference. After questioning supervisors and clinicians, we did not find any similar cases among other employee groups or inpatients. We surveyed all employees who had attended the conference about the nature and timing of symptoms and the specific food items that were eaten at the conference. Based on the high prevalence of vomiting among symptomatic employees, we defined cases as individuals who developed vomiting after attending the conference and controls as individuals who attended the conference but denied subsequent vomiting or diarrhea. We calculated the odds of symptomatic illness associated with the consumption of individual food items at the conference.
METHODS The Department of Behavioral Health at the Philadelphia VA Medical Center held its weekly grand rounds conference, at which
RESULTS
* Address correspondence to Christopher Vinnard, MD, MPH, MSCE, Division of Infectious Diseases, University of Pennsylvania School of Medicine, 502 Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104. E-mail address: [email protected] (C. Vinnard). A portion of this work was presented as an abstract at the Annual Scientific Meeting of the Society for Healthcare Epidemiology of America, March 2011. C.V. received salary support through a National Institutes of Health Institutional Research Training Grant (T32). Conflicts of interest: None to report.
We obtained 63 surveys from conference attendees, including 23 individuals who reported vomiting and 35 individuals who reported no symptoms. Five individuals reported symptoms that did not include vomiting and were excluded from the analysis. Two symptomatic employees with diarrhea presented to Occupational Health, and both had stool specimens that were positive for norovirus by nucleic acid testing and negative for all bacterial pathogens tested.
0196-6553/$36.00 - Copyright Ó 2012 by the Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.ajic.2011.03.033
74
C. Vinnard et al. / American Journal of Infection Control 40 (2012) 73-4
Table 1 Odds of symptomatic illness associated with specific food items
Food item Ham sandwich Ice Potato chips Turkey sandwich Chocolate chip cookies
Cases (N ¼ 23), n (%) 12 12 15 8 12
(52) (52) (65) (35) (52)
Controls (N ¼ 35), n (%) 2 5 8 5 11
(6) (14) (23) (14) (31)
OR (95% CI) 18.0 6.5 6.3 3.2 2.4
(3.1-179.0) (1.6-28.6) (1.7-24.0) (0.8-14.5)* (0.7-8.1)*
*Not significant (P > .05).
The individual food items with a significant odds ratio (OR) for illness included ham sandwich (OR, 18; 95% confidence interval [CI], 3-179), ice (OR, 7; 95% CI, 2-29), and potato chips (OR, 6; 95% CI, 2-24) (Table 1). Both the ice and the chips came from shared open containers. Seven individuals attended the conference but did not eat, and none of these individuals developed symptoms. After our investigation, the city Health Department was notified, and the caterer was evaluated. The Health Department informed us that there were no significant health code violations, but could not report to us whether there were any ill employees. We initiated several infection control measures. Hand hygiene was reinforced among all employees. A phenolic cleaning agent (Ready-To-Use Wex-Cide; Wexford Labs, Kirkwood, MO) was used to clean the room in which the grand rounds conference was held, at concentrations viricidal against norovirus. All symptomatic employees were sent home, and were instructed to remain at home until 72 hours after symptoms resolved. Daily reviews with supervisors and clinicians were conducted after notification of the infection control team, and no secondary cases of norovirus gastroenteritis were identified among either hospital employees or patients. DISCUSSION A recent meta-analysis found no evidence that infection control interventions shortened the duration of norovirus outbreaks (22 days when infection control measures were implemented vs 18 days without specific measures).6 Several factors likely contributed to the success of our efforts in containing this outbreak of norovirus gastroenteritis. First, the infection control team was notified within 1 day of the first report of symptoms, and previous work has shown that timely identification of nosocomial transmission is essential for containing a norovirus outbreak.5 Rapid
decontamination of the outbreak site with terminal cleaning agents is also critical, given the central role of environmental surface contamination in the propagation of norovirus outbreaks.7 In addition, all sick employees were instructed to remain at home until asymptomatic for 72 hours, limiting contact of infected employees with uninfected employees and patients during the period of greatest infectivity. Finally, the outbreak was associated with a conference setting rather than a patient care location (although many of the conference attendees had clinical responsibilities). Both presymptomatic and postsymptomatic individuals have been implicated as sources of norovirus outbreaks, and norovirus shedding among asymptomatic food handlers has been documented.8 Based on the multiple food sources identified in the casecontrol study, we suspect that contamination with norovirus occurred either at the site of preparation by a food handler or during the distribution of food before the conference. One limitation of our study is that we were unable to determine whether ill employees had been involved at any stage of food preparation or delivery. In summary, our investigation highlights the potential for multiple food source contamination with norovirus, and demonstrates the success that a multifaceted infection control strategy can have in preventing the transmission of norovirus from infected hospital staff to uninfected hospital staff and patients.
References 1. Scallan E, Hoekstra RM, Angulo FJ, Tauxe RV, Widdowson MA, Roy SL, et al. Foodborne illness acquired in the United States: major pathogens. Emerg Infect Dis 2011;17:7-15. 2. Teunis PF, Moe CL, Liu P, Miller SE, Lindesmith L, Baric RS, et al. Norwalk virus: how infectious is it? J Med Virol 2008;80:1468-76. 3. Marks PJ, Vipond IB, Carlisle D, Deakin D, Fey RE, Caul EO. Evidence for airborne transmission of Norwalk-like virus (NLV) in a hotel restaurant. Epidemiol Infect 2000;124:481-7. 4. Glass RI, Parashar UD, Estes MK. Norovirus gastroenteritis. N Engl J Med 2009; 361:1776-85. 5. Johnston CP, Qiu H, Ticehurst JR, Dickson C, Rosenbaum P, Lawson P, et al. Outbreak management and implications of a nosocomial norovirus outbreak. Clin Infect Dis 2007;45:534-40. 6. Harris JP, Lopman BA, O’Brien SJ. Infection control measures for norovirus: a systematic review of outbreaks in semi-enclosed settings. J Hosp Infect 2010; 74:1-9. 7. Wu HM, Fornek M, Schwab KJ, Chapin AR, Gibson K, Schwab E, et al. A norovirus outbreak at a long-term-care facility: the role of environmental surface contamination. Infect Control Hosp Epidemiol 2005;26:802-10. 8. Okabayashi T, Yokota S, Ohkoshi Y, Ohuchi H, Yoshida Y, Kikuchi M, et al. Occurrence of norovirus infections unrelated to norovirus outbreaks in an asymptomatic food handler population. J Clin Microbiol 2008;46:1985-8.