What Is the Incubation Period for Listeriosis?

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


BMC Infect Dis. 2013;13(11) 

In This Article


Listeriosis is an uncommon bacterial infection that is potentially fatal in the foetus, in newborns and immunocompromised adults. Listeria monocytogenes (Lm) cause invasive listeriosis with central nervous system involvement (meningitis, meningoencephalitis) and bactaeremia with a high case fatality rate (20% to 30%).[1,2] Lm also cause non-invasive disease such as gastroenteritis.[3] Lm is widely distributed in the environment and can contaminate a wide variety of foods.[4,5] Lm has the ability to grow at low temperatures (+4°C) and is destroyed by heat. The epidemiology of listeriosis has been partly elucidated since the 1980's, when foodborne transmission was established.[6,7] Vehicles of transmission of Lm are mostly ready-to-eat foods.[5]

In infected hosts, Lm crosses the intestinal epithelium barrier via transcytosis and invades the mesenteric lymph nodes and the blood.[8] The majority of bacteria become trapped in the liver and therefore are rapidly cleared form the circulatory system. Surviving bacteria replicate in hepatocytes. Early recruitment of polymorphonuclear cells leads to hepatocyte lysis, and thereby bacterial release. If the infection is not controlled at this stage, for instance because of severe immunodepression, a secondary bacteraemia develops. Bacteria circulating in the blood, either free or associated with leucocytes are disseminated to sanctuary sites by transgressing the blood-brain barrier or the placental barrier.[9] In pregnant hosts the bacteria can probably cross the endothelium of the maternal blood-vessels, followed by the entry into the fetal circulatory system of the placental villi.[10]

In foodborne diseases the incubation period is the delay between the consumption of a contaminated product and the onset of first symptoms of the disease. Unlike common food borne diseases such as salmonellosis, the incubation period of listeriosis can be long. Multiple aspects of listeriosis make the determination of a precise incubation period difficult. Firstly, Lm can contaminate a large variety of foods, which hinders the identification of an infected food source. Secondly, as the incubation period is thought to be variable and long, products consumed during a long period (usually 30 days) are suspected. Thirdly, many products contaminated by Lm are products that can be kept during several days or weeks and can therefore be eaten by the patient on multiple occasions. Therefore data on incubation period referring to single exposures are scarce. The first data on the incubation period for listeriosis were published in 1987 about a Californian outbreak associated with cheese that involved more than 100 cases.[6] Linnan reported already the difficulty in identifying sufficient cases with a single exposure from which an incubation period could be calculated. He subsequently identified a median incubation period of 31 days (range, 11 to 70) in four patients with single exposure.

Since this outbreak, authors of scientific publications and text books for epidemiologists and clinicians refer to this incubation period.[11,12] In 2006, in a paper on a nationwide outbreak associated with frankfurters involving 108 cases in the United States of America, Mead mentioned that in this outbreak "the average incubation period for invasive listeriosis is shorter than generally assumed" but could not document it more accurately as many patients had recurrent exposures to the implicated product.[13]

Our study aimed to estimate precisely the incubation period of listeriosis using available published data and data obtained during outbreak investigations carried out by the Institut de Veille Sanitaire (French Institute for Public Health Surveillance, InVS). Our goal is to enhance the efficiency of investigations targeted towards identifying foods at the origin of listeriosis outbreaks by documenting as precisely as possible the incubation period, for the different forms of invasive listeriosis.