LISTERIOSIS

Listeria monocytogenes—an uncommon human pathogen of animal origin—has some unusual properties. The organism is widespread in the environment and many animals, and has the ability to grow over a temperature range (2-42°C) that includes refrigerator temperatures. . . . The bacterium itself becomes intracellular and has an outstanding predilection for pregnant women, in whomit causes very slight or inapparent illness but may cross the placenta to kill the fetus or give rise to perinatal septicaemia or meningitis in the newborn baby.... Listeria spp are present in vegetation, water, soil, and the faeces of man and animals, so it is not surprising that they are present in food. It follows that ingestion of modest numbers of listeria causes no clinical problems in healthy people.... The infective dose is also unknown, but presumably it is lower for pregnant and immunologically compromised individuals than for the normal population.... What is very clear is that as produced, processed, and finally cross-contaminated in chicken packing plants, very nearly all chicken carcasses are contaminated with listeria, as well as with Campylobacter jejuni and salmonellae. In the past two or three years infections due to these microbes have increased almost exponentially; they are all sporadic in distribution, and all three organisms are frequently introduced into the environment of the domestic kitchen via chicken meat.... There is always complacency in the livestock industry when infective agents do not cause significant economic losses in flocks or herds—listeria, salmonellae, and campylobacters all fail to do this. Surely it is time to think of the effect on human beings.