Clinical Practice Guidelines Antenatal Care — Module II
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- Prevalence and incidence
- Risks associated with toxoplasmosis during pregnancy
- Screening for toxoplasmosis
- Diagnostic accuracy of tests
- Harms and benefits of screening
- Availability of safe and effective treatments
- Discussing toxoplasmosis
- Practice summary: toxoplasmosis
9.7ToxoplasmosisThere is limited evidence to support screening for toxoplasmosis during pregnancy. As infection may be transmitted to the baby during pregnancy, the focus is on providing women with advice about how to avoid sources of toxoplasmosis. BackgroundToxoplasmosis, which is caused by the parasite Toxoplasma gondii, is usually asymptomatic and self-limiting. Symptoms when they occur include swollen lymph nodes, muscle aches and pains and fever. When women who have not previously been exposed to the parasite (eg are non-immune) become infected during pregnancy, the infection can be transmitted to the baby (Di Mario et al 2009). The likelihood of a woman acquiring a primary infection during pregnancy varies, depending on local prevalence (Pappas et al 2009): low prevalence: the potential for a woman to become infected is low but if she is infected during pregnancy it will most likely be a primary infection; and high prevalence: primary infection during pregnancy is unlikely due to previous exposure. Toxoplasmosis infection can be acquired by (Di Mario et al 2009): eating raw or insufficiently cooked meat; not washing hands thoroughly after handling raw meat or gardening; contact with cat faeces (directly or indirectly through the soil or cat litter); or contact with contaminated raw vegetables or fruits. Prevalence and incidenceIn Australia, primary infection with toxoplasmosis during pregnancy is rare (Gilbert 2002) although it is estimated that between 60% and 80% of Australians are non-immune (Pappas et al 2009). Country of origin: The prevalence of immunity to toxoplasmosis is high in Latin America, parts of Eastern/Central Europe, the Middle East, parts of South-East Asia and Africa. There is a trend towards lower prevalence of immunity in many European countries and the United States (Pappas et al 2009). Congenital toxoplasmosis: The incidence of congenital toxoplasmosis has been reported to range from 0.03/1,000 live births in England and Wales (Gilbert et al 2006) to 0.3/1,000 live births in south-eastern Brazil (Carvalheiro et al 2005). Risks associated with toxoplasmosis during pregnancyMother-to-child transmission rates have been reported to range from 11.3% (Ricci et al 2003) to 18.5% (Varella et al 2009). The risk of transmission increases with gestational age (from 5% at 12 weeks to 80% just before birth) (Dunn et al 1999). However, babies infected early in pregnancy have a greater risk of congenital anomalies (Di Mario et al 2009). Congenital toxoplasmosis has been associated with stillbirth, intracranial anomalies and/or developmental delay, ocular inflammation (Gilbert et al 2006) and impaired hearing (Andrade et al 2008; Brown et al 2009). In a prospective cohort study (n=620), babies with congenital toxoplasmosis had lower gestational age but there was no significant association with low birth weight or small for gestational age (Freeman et al 2005). Screening for toxoplasmosisSummary of the evidenceThe evidence on the benefits to women and babies of screening for toxoplasmosis is limited and inconclusive. Routine screening for toxoplasmosis during pregnancy is not recommended in the United Kingdom (NICE 2008). Diagnostic accuracy of testsScreening tests for toxoplasmosis aim to identify whether maternal infection is acute or chronic. Studies have compared a range of tests for IgG and IgM antibodies and IgG avidity (Petersen et al 2005; Thalib et al 2005; Flori et al 2008; Bobic et al 2009; Kasper et al 2009; Lachaud et al 2009; Elyasi et al 2010; Wallon et al 2010; Jost et al 2011; Lesle et al 2011; Robert-Gangneux et al 2011; Yamada et al 2011). There is great heterogeneity between the studies, making it difficult to comment on the predictive and diagnostic accuracy of one test over another. Studies into the timing of screening are limited and inconclusive (Gilbert & Gras 2003). No evidence on the cost-effectiveness of screening for toxoplasmosis was identified. Harms and benefits of screeningNo high-level evidence on the harms and benefits of screening for toxoplasmosis was identified. A narrative review found that psychological consequences of screening included parental anxiety due to false positive results and uncertainties related to prognosis of children with an antenatal diagnosis of congenital toxoplasmosis (Khoshnood et al 2007). Recommendation 27 Grade C Do not routinely offer screening for toxoplasmosis to pregnant women.
A systematic review (Thiébaut et al 2007) found weak evidence for an association between early maternal treatment and reduced risk of congenital toxoplasmosis. A subsequent review (Peyron et al 2010) concluded that despite the large number of studies performed, it is still not known whether treatment of pregnant women with presumed toxoplasmosis reduces the transmission of T. gondii. While some studies have reported a lack of symptoms among babies whose mothers were treated during pregnancy (Berrébi et al 2007; 2010; Cortina-Borja et al 2010), current research is inadequate to assess whether the possible benefits outweigh the potential harm to the baby from treatment (Peyron et al 2010).
Recommendation 28 Grade C Advise pregnant women about measures to avoid toxoplasmosis infection such as: • washing hands before handling food; • thoroughly washing all fruit and vegetables, including ready-prepared salads, before eating; • thoroughly cooking raw meat and ready-prepared chilled meals; • wearing gloves and thoroughly washing hands after handling soil and gardening; and • avoiding cat faeces in cat litter or in soil. Practice summary: toxoplasmosis
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