What Is the Incubation Period for Listeriosis?

Véronique Goulet; Lisa A King; Véronique Vaillant; Henriette de Valk

Disclosures

BMC Infect Dis. 2013;13(11) 

In This Article

Methods

We searched in PubMed, papers published between January, 1980, and January, 2012 (inclusive), using the terms ((Disease outbreaks OR cross-infection OR Clusters) AND (listeriosis OR listeria monocytogenes)) AND (Food OR investigation).

By reviewing the 288 retrieved records, we identified 42 reports on outbreaks or clusters of listeriosis, and among them 16 reports documenting food borne point-source listeriosis outbreaks. Additional documented food-borne listeriosis cases or clusters were identified by reviewing the reference lists of the retrieved reports (n=3). Furthermore, we reviewed french listeriosis investigation reports of the Institut de Veille Sanitaire and identified data on incubation period in three reports of unpublished outbreaks and one report of a sporadic foodborne case.

A precise incubation period was defined as the delay between the date of consumption of a contaminated food and the date of onset of clinical symptoms or, if not available, of the date of the first Lm positive biological sample taken from the patient.

We reviewed the selected 23 reports to identify cases with a documented incubation period, calculated when a patient had a single exposure to a confirmed food source of contamination. The estimated incubation period of cases with multiple consumptions or with no precise date of consumption (i.e. date of purchase of the contaminated product) were classified as "approximate incubation period".

Cases of invasive listeriosis were classified as:

  • cases with central nervous system involvement (CNS cases): Lm isolated from cerebrospinal fluid (CSF), or from blood in a patient with clinical symptoms of CNS involvement

  • bacteraemia cases: Lm isolated from blood cultures with no clinical symptoms of CNS involvement

  • pregnancy-associated cases: Lm isolated in blood from a pregnant woman, or in samples from placenta, a foetus, a stillbirth, or a newborn less than one month of age.

Cases of listeria gastroenteritis were defined as:

  • cases with gastrointestinal symptoms and Lm isolates recovered from stool.

  • or cases with gastrointestinal symptoms epidemiologically linked to cases of listeriosis confirmed by Lm isolation.

Results are expressed as a median [range] for continuous variables. Associations between quantitative and qualitative variables were assessed using the Kruskal-Wallis test. Statistical analysis and box plots were performed using Stata8®. For each clinical form of invasive listeriosis, we calculated the median incubation period and the first and the third quartile (in days). For gastroenteritis cases, we report for each outbreak, the number of cases, the median and the range of the incubation period (in hours).

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