Pregnant women have a 20 times higher risk of listeriosis than the general population and account for a third of all confirmed cases. Three cases of listeriosis in pregnancy, reported during an outbreak in Canada caused by contaminated cheese, are a reminder of this uncommon but potentially lethal condition.

The first patient, a 35-year-old primigravida, presented with fever and preterm labour at 29 weeks' gestation. The baby was delivered by caesarean section. Both she and her mother were treated with antibiotics. The infant showed no evidence of infection.

The second patient, presented at 24 weeks' gestation, with fever, decreased fetal movements and regular uterine contractions. After discussion, the woman proceeded to labour spontaneously. Because of the extremely poor prognosis resuscitation was not attempted at delivery and the infant died within the hour.

The third patient recalled having a fever two weeks previously. She presented at 35 weeks' gestation with abdominal pain, vaginal bleeding and decreased fetal movements. As in the first case the infant was delivered in good condition by caesarean section and mother and baby were successfully treated with antibiotics.

The clinical pictures presented were remarkably non-specific. None of the patients recalled eating any suspicious food. Listeria does not taint the food it contaminates so contaminated food has no particular smell, colour or taste. All three pathogens were of the same strain as the organism causing the contaminated cheese outbreak.

The Quebec outbreak resulted in 36 severe infections, 13 in pregnant women, with five neonatal infections. There were two cases of fetal demise and one early neonatal death. All occurred at <25 weeks' gestation.

Listeria monocytogenes is ubiquitous. It causes serious morbidity and mortality in the immunocompromised and in pregnancy to both mother and baby. In the later stages of pregnancy women have reduced cellular immunity and thus are more susceptible to infection.

As GPs it is up to us to give advice to prevent this foodborne infection (avoid undercooked meat, preprepared foods, leftovers and foods made from unpasteurised milk). We also have to maintain a high index of suspicion when dealing with febrile pregnant patients. Thankfully, listeriosis usually responds well to antibiotic therapy.

Dr Chris Barclay