Ingestion of Lm is a very common occurrence (1
) since it has been isolated from many food products in Israel (unpub. data, MOH) as well as in many countries worldwide. Development of invasive disease secondary to Lm ingestion is determined primarily by the integrity of the immune system of the host (predominantly cell-mediated immune defects) and possibly also by inoculum size (11
). The organism crosses the mucosal barrier of the intestine and invades the bloodstream. It may disseminate to any organ, but it has a clear predilection for the placenta and CNS, thereby determining the main clinical syndromes.
The case-fatality rate in the collected data on perinatal infection was 36% (413 of 1,149 patients for whom this information was available). This high mortality reflects both the severity of Lm infection and the seriousness of the underlying conditions. Higher mortality rates were correlated with older age, presence of CNS infection, and immunodeficiency (5
). One study reported that deaths in immunocompetent patients occurred exclusively in the elderly (9
), a finding that correlates well with our observations.
An unexpected observation in our study was the occurrence of hospital-acquired listeriosis in adults. The presumed hospital acquisition occurred on day 3-67 of hospital stay in 59 (16%) of 369 cases with relevant information, as reported in four studies, including ours (9
). All patients acquiring listeriosis in the hospital (except one) were immunocompromised. No clustering of cases in time or place occurred, and no case had an obvious source for nosocomial acquisition of Lm. Because the incubation period of listeriosis is long (11-70 days) and fecal carriage not uncommon (5%-10%) (1
), colonization could have been acquired before hospitalization and infection developed in the hospital, possibly even triggered by increased immunosuppression. Another possible explanation is consumption of contaminated food brought in from sources outside the hospital, but this could not be documented. We found only one description of a hospital outbreak of Lm among adults (three cases secondary to an index one), but the method of transmission was not established (22
). Hospital transmission among neonates in nurseries was thought to occur more frequently (24%) (12
) and was described by several investigators (18
Among perinatal infections, we report the highest case-fatality rate (45%). This observation could be related to the frequency of taking cultures from aborted tissues. The diagnosis of Lm can easily be missed if cultures are not routinely taken from aborted fetal tissues or if blood (and other) cultures are not obtained from febrile pregnant women. The great variability in incidence rates and other epidemiologic features between studies and among medical centers within studies suggests that many cases escaped diagnosis.
Concerning the mothers, all authors described a mild febrile “influenzalike” illness, without maternal deaths. Only one of the 494 mothers had meningoencephalitis with Lm isolated from the cerebrospinal fluid, but underlying condition or maternal and fetal outcomes were not reported (12
). Eight mothers (<2%) were immunocompromised (), but no comparable data are available on the prevalence of these conditions among pregnant women in general.
In conclusion, listeriosis is an emerging zoonosis that constitutes a life-threatening disease for human fetuses and neonates, the elderly, and patients with certain predisposing conditions. Documented cases may not represent the true incidence in the community, especially with regard to perinatal infection. Fetal and maternal cultures should be obtained in every case of spontaneous abortion or stillbirth, to ensure proper diagnosis. Empiric ampicillin therapy should be included in the treatment of neonatal meningitis, sepsis, or meningitis in the elderly and immunocompromised patients and in febrile pregnant women without a source of infection.