A large outbreak of Listeria monocytogenes infection with short incubation period in a tertiary care hospital
Introduction
Listeria monocytogenes is a ubiquitous organism with growth abilities exceeding the ordinary human pathogen, being able to multiply at refrigerator temperatures. This agent is an unusual, but dreaded cause of foodborne infection, due to its high mortality rate.1, 2, 3, 4L. monocytogenes is now recognised as a cause of gastroenteritis.5, 6 However, exposure to this organism probably occurs frequently and a transient intestinal carrier state is common in the healthy human population.7, 8 Life-threatening disease is primarily seen in neonates and in immunocompromised patients.1, 8 Infection of the central nervous system (CNS) and septicaemia are the most common forms of invasive disease.1, 3, 8
Outbreaks of foodborne L. monocytogenes infections have previously been reported.2, 9 They have also been observed in hospitals, but previous outbreaks have mostly been small.10, 11, 12, 13, 14, 15, 16, 17 Often, no source of infection has been found, presumably due to a long incubation period. Today, there are large specialised hospital facilities for immunocompromised patients. To our knowledge only two Listeria outbreaks with an identifiable source have so far been reported in such a setting.18, 19
We report here a large outbreak of L. monocytogenes in a tertiary care hospital with a high proportion of immunocompromised patients.
Section snippets
Identification of patients and clinical data
Cases were defined as follows: Persons admitted to or working at Rikshospitalet University Hospital in the period September 28, 2007 to October 12, 2007 with the presence of L. monocytogenes demonstrated in a normally sterile site, or with L. monocytogenes isolated from faeces when diarrhoea and fever were present. Consequently, asymptomatic faecal carriers detected during the outbreak investigation were not included. For pregnant women, only the mother was considered a case, while fetal
Results
At the time of the outbreak, Rikshospitalet University Hospital was an 860-bed hospital including a comprehensive cancer centre and Norway’s only transplantation centre. The outbreak affected a total of 17 patients with L. monocytogenes infection, 11 females and 6 males with median age of 64 years (range: 27–84).
For characteristics of the patients and their predisposing conditions, see Table 1. All but 2 patients (88%) had predisposing underlying conditions and/or received immunomodulating
Discussion
Listeriosis is well known to occur in outbreaks. This is a report of a large, nosocomial outbreak in one hospital involving 17 patients. All patients fell ill during a 32-day period. The estimated attack rate was low, but the mortality rate was high and the incubation period was surprisingly short. The source of the outbreak was a Camembert cheese made from pasteurised milk.
Previous outbreaks of listeriosis in hospitals have been reported.10, 11, 12, 13, 14, 15, 16, 17, 18, 19 Most of these
Financial support
None.
Potential conflict of interest
Bjørn O. Johnsen has received research funding from The Norwegian Surveillance Programme for Antimicrobial Resistance and has received funds for travel from Wyeth.
Egil Lingaas has received funds for travel from Wyeth, 3M and Mölnlycke Healthcare.
Dag Torfoss has received funds for travel from Amgen, Roche and Wyeth.
Erik H. Strøm has no conflicts of interest.
Ingvild Nordøy has received funds for travel from Gilead Sciences and MSD.
Acknowledgments
We thank Georg Kapperud and coworkers at the Department of Food-borne Infections at the NIPH for serogrouping and MLVA-typing the L. monocytogenes isolates. We are also grateful to Eivind Ragnhildstveit, Department of Microbiology, Østfold Hospital, Fredrikstad, Raisa Hannula, Department of Medical Microbiology, St. Olavs Hospital, Trondheim University Hospital, Trondheim, and Anne-Lise Bruu, Department of Microbiology, Vestfold Hospital, Tønsberg, for sending isolates of L. monocytogenes from
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