Sources of toxoplasma infection in pregnant women: European multicentre case-control study

Congenital toxoplasmosis is an established cause of intrauterine death and severe neonatal disease. Later effects of this infection include learning difficulties and ocular disease. Several countries, notably France and Austria, have introduced national prenatal screening programmes in an attempt to reduce the incidence of this condition. In other countries, harm to benefit analysis has suggested that universal screening is unlikely to be beneficial.1-1 Subsequently, attention has moved to primary prevention—the elimination of toxoplasma infection in the pregnant woman. Toxoplasma infection is acquired by ingestion of one of the life forms of the parasite that contaminate meat, soil, vegetables, milk, or water. The relative importance of these routes of transmission is poorly defined so that compliance with health education aimed at reducing exposure is problematic.1-2 Cook and colleagues report the results of a multicentre, European study of risk factors for the acquisition of acute toxoplasmosis during pregnancy. Knowledge of the different routes of transmission was shown to vary, but eating undercooked, raw, or cured meat, contact with soil, and travel outside of Europe or the US and Canada were found to be significantly associated with maternal infection in all countries. The multicentre nature of the study allowed the investigation of a large population of cases and controls in a relatively short period, thus reducing the risk of selection of an unrepresentative study group and the effect of changes in routes of transmission over time. The European approach was also associated with several problems. Each centre used different laboratory tests to identify acute maternal infection, one centre tested women after delivery whereas the others tested during the pregnancy, telephone interviews were replaced by face to face interviews for cases and some controls at one centre, and knowledge of risk factors was not considered at one location. Inconsistent methodology may have introduced unrecognised bias. All investigators and women studied were aware of the toxoplasma status before the interview. Many control women correctly stated that consumption of inadequately washed salads and raw vegetables was a risk factor for acquiring toxoplasma infection. This route of transmission, however, was not considered in detail at interview and may explain, at least in part, the failure to identify the likely route of infection in up to half of cases. One hundred and fifty eligible control women did not complete an interview because of contact failure, inability to speak the local language, or refusal to participate. In contrast all 252 infected women (cases) completed the study. This clear difference may be significant given the association between travel outside Europe and acute toxoplasma infection detected in the study. Despite these limitations, the paper has important implications for the control of congenital toxoplasmosis. Preventive strategies are required to reduce the infectivity of meat products. Current health education may benefit from focus and refinement, concentrating on principal risk factors at the expense of less important issues,1-3 and the health implications of consuming raw, undercooked, or cured meats in pregnancy require careful consideration.