Simultaneous serological screening for congenital cytomegalovirus and toxoplasma infection

Prevention of congenital toxoplasmosis

In utero infection with Toxoplasma gondii may result in congenital defects such as hydrocephalus, chorioretinitis and mental retardation; these defects may be present at birth or may develop later in life. Prevention of this disease can be achieved in different ways. The most effective measure is to prevent the acquisition of the disease during pregnancy by avoiding risk factors for Toxoplasma gondii infection. Health education may decrease the incidence of toxoplasmosis during pregnancy by 60%. A second preventive measure is based on serologic screening during pregnancy to identify infected women. Treatment during pregnancy results in a significant reduction in the incidence of sequelae including severe handicaps. A third possible intervention is treating infected neonates. Antibiotic treatment of infected children has a beneficial effect on the development of sequelae and the sooner therapy is started after birth, the better the outcome. This overview presents the potential benefits and harms of these different options available for the prevention of congenital toxoplasmosis.

Toxoplasma antibody titers by ELISA and indirect latex agglutination test in pregnant women

The seroepidemiologic studies on anti-Toxoplasma antibody titers were carried out using ELISA and indirect latex agglutination test. Among 899 sera prepared from pregnant women, 39 cases (4.3%) revealed positive reaction and 218 sera from middle school students showed 4 positive reaction (1.8%) by ELISA. By LAT (newly established by National Veterinary Research Institute. Korea), the sera of 7 pregnant women (0.8%) showed positive reaction. When 80 sera showing > or = 1:8 by LAT were used for comparing the results obtained from LAT and Toxotest-MT (Eiken Chemical Co., Japan), 7 cases and 8 sera were positive, respectively. All of 11 sera of proven toxoplasmosis patients showed positive reaction in both tests. Overall proportion of agreement between LAT kit and Toxotest-MT was 0.94 (kappa-index = 0.632, p < 0.011, and LAT was considered to be useful for the screening of toxoplasmosis.

Low incidence of primary infection with toxoplasma among women in Sheffield: a seroconversion study

OBJECTIVE

To determine the incidence of primary toxoplasma infection in women of childbearing age.

DESIGN

A retrospective study of seroconversion on stored pairs of sera taken for routine antenatal testing.

SETTING

The antenatal clinics and general practices of Sheffield between July 1989 and October 1992.

SUBJECTS

One thousand six hundred and twenty-one women on whom pairs of sera, separated by more than 500 days, had been received.

MAIN OUTCOME MEASURE

Rate of primary infection determined by seroconversion as measured by the presence of antibody in the second serum and its absence in the first.

RESULTS

Of 1621 women, 160 (9.9%) were initially seropositive. One seroconversion was detected in 2966 woman years of observation for susceptibles. The projected rate for primary infections was 0.23 (95% CI 0.0059-1.3) per 1000 pregnancies.

CONCLUSIONS

The rate is much lower than for earlier estimates of incidence in the UK but agrees with a more recent estimate from Sheffield and suggests a falling incidence.

Incidence of acute symptomatic toxoplasma retinochoroiditis in south London according to country of birth

OBJECTIVE

To determine the incidence of acute symptomatic toxoplasma retinochoroiditis presenting to ophthalmologists for patients born in Britain and elsewhere.

DESIGN

Population based, cross sectional study.

SETTING

11 districts in south Greater London.

SUBJECTS

All patients presenting to NHS ophthalmologists with symptoms due to acute toxoplasma retinochoroiditis in 1992-3.

MAIN OUTCOME MEASURE

Intraocular inflammation in association with a retinochoroidal scar, active adjoining retinitis, and IgG serum antibodies to toxoplasma.

RESULTS

The estimated incidence of acute symptomatic retinochoroiditis for all people born in Britain was 0.4/100,000/year. If a mean of two symptomatic episodes per lifetime is assumed, 100 people born in Britain may be affected each year, about a fifth of the estimated 500-600 congenitally infected people born each year.

CONCLUSIONS

A substantial proportion of people with acute symptomatic toxoplasma retinochoroiditis were born outside the country, and the number born in Britain was smaller than the number previously estimated to develop retinochoroidal lesions due to congenital toxoplasmosis. These findings suggest that prenatal screening for toxoplasmosis in Britain may be of limited benefit.

Toxoplasma gondii--an unusual cause of myocarditis in old age

We report the case of an 86-year-old man who was admitted with congestive cardiac failure and chronic renal failure. He was previously known to have a thoracic aortic aneurysm and chronic bronchitis. There was no history of myocardial infarction but his heart failure was assumed to be due to ischaemic heart disease. Despite treatment of the heart failure the patient died. At post-mortem he was found to have Toxoplasma gondii myocarditis.

Toxoplasmosis in pregnancy

Primary infection with Toxoplasma gondii in pregnant women occurs all over the world with frequencies between 0.1-1%. In approximately 40% of the cases, the unborn child is infected. The risk of fetal infection increases during pregnancy, while at the same time the risk of severe disease decreases. As a result, infants with congenital toxoplasmosis are mostly asymptomatic at birth, but long-term studies indicate that up to 85% of them will develop sequelae including chorioretinitis (leading to severe impairment of vision), hearing loss or mental retardation. Early recognition of maternal infection and treatment with spiramycin or pyrimethamine-sulphadiazine will reduce the parasitic colonization of the placenta by more than 60% and prevent infection in the fetus. If fetal infection has already occurred, maternal treatment modifies the fetal disease. Therapy during the first year of life improves the prognosis. It is possible today to identify infected fetuses by prenatal diagnosis based on detection of the parasite in cord blood, amniotic fluid and placental tissue. Specific antibodies and non-specific signs of infection in fetal blood give additional information. Advances in laboratory techniques have made it feasible to consider serological surveillance of pregnant women. The present recommendation is that each country should provide data on the incidence of toxoplasma infection in pregnancy and thereby decide whether it represents a problem and what measures should be adopted. This paper summarizes the present knowledge of the parasite and its implication for the mother and unborn child. The effect and problems of primary and secondary prevention in pregnancy are discussed as well as the efficacy of treatment. The need for future research including long-term follow-up studies are emphasized.

Methods for estimating the incidence of primary infection in pregnancy: a reappraisal of toxoplasmosis and cytomegalovirus data

Accurate incidence information is required to plan and evaluate screening programmes which have been proposed for the detection of primary toxoplasmosis and cytomegalovirus infection in pregnancy. Appropriate statistical methods are described for deriving incidence rates and their confidence intervals from three types of data: change in age-specific seroprevalence, seroconversion, and IgM studies. These methods are applied to seven published studies on toxoplasmosis and cytomegalovirus carried out in the UK. In these publications only one estimate of the infection rate per pregnancy was correctly derived, and none were accompanied by confidence intervals. Using the proposed methods, most estimates of the primary toxoplasmosis rate in these studies were between 2.5 and 5.5 per 1000 pregnancies, compared to the 2 per 1000 usually cited. Most cytomegalovirus incidence estimates were between 4 and 10 per 1000 pregnancies.

Longitudinal study of Toxoplasma seroprevalence in South Yorkshire

Serum samples collected from individuals of a wide range of ages in South Yorkshire between 1969 and 1990 provided the basis for a longitudinal seroprevalence survey of Toxoplasma gondii antibodies. Sera numbering 3868 were screened for T. gondii specific antibodies using a commercial latex agglutination test. The resultant temporal series of serological profiles revealed a rise, with age, in seroprevalence, the rate of which showed a decrease through time. A plateau of around 40-50% prevalence was attained by the 41- to 45-year age-class in 1969 which was not approached until the 66- to 70-year class in the 1988-90 data set. This trend for decline in seroprevalence was confirmed by statistical analysis for the age range 21-60 years. These results may be indicative of a decrease in the rate of toxoplasma exposure in this study community over the 20-year period. The survey of 1988-90 provides a base-line profile of present-day seroprevalence in which 11% of individuals in the age range 16-45 years (roughly corresponding to the childbearing age-range) show evidence of past infection. The representative nature of the serum collection and public-health implications of these results are discussed.

Evaluating the sensitivity and predictive value of tests of recent infection: toxoplasmosis in pregnancy

The diagnosis of maternal infection in early pregnancy depends on tests which are sensitive to recent infection, such as specific IgM. Two types of test are considered: those where the response persists for a period following infection and then declines, such as IgM, and those whose response increases with time since infection, such as IgG-avidity. However, individuals vary in their response to infection, and it may not always be possible to determine whether an infection occurred during pregnancy or before it. Mathematical methods are developed to evaluate the performance of these tests, and are applied to the diagnosis of toxoplasmosis in pregnancy. It is shown that, based on existing information, tests of recent infection are unlikely to be both sensitive and predictive. More data on these tests are required, before they can be reliably used to determine whether infection has occurred during pregnancy or before it.

Congenital toxoplasmosis: to screen or not to screen?

We have reviewed the present day quantifiable cost to society of the 73 cases of congenital toxoplasmosis which are estimated to occur annually in Scotland with the cost of preventing the disease by screening and treatment. Our analysis includes advances in laboratory techniques. The cost of screening would depend on its scale and if in-house or commercial tests are used. If only 2 specimens were screened, at booking and at delivery, the screening costs are estimated to be between 0.5-0.9 times the preventable costs. If a third specimen were tested in the second trimester, to maximise scope for remedial action during pregnancy, the screening costs are 0.7-1.2 times preventable costs. As likely screening costs in most of the schemes we consider are now less than the preventable costs, a screening programme should be adopted.

Diagnosis of congenital toxoplasmosis in Scotland

During a period of 10 years (1976-1986) 853 cases of toxoplasmosis were identified serologically in the Toxoplasma Reference Laboratory in Scotland. Suspected cases of infection in pregnancy (29 cases) and of congenital infection (27 cases) were rare but ophthalmic disease was common (224 cases). In two of the congenital cases, maternal infection was identified during pregnancy. The other 25 babies were investigated because of suspected congenital infection. Toxoplasmosis was confirmed retrospectively in 11/25 babies and excluded in two of them. The other 12 cases remain unclassified. Diagnosis of infection in babies was difficult although the introduction of an IgM capture ELISA was of some help. IgM was detected by ELISA in 3/13 congenitally infected babies but by immunofluorescence tests in only one of these. In two antenatal studies, involving 16,000 women, an additional 32 women were identified whose babies might have benefited from treatment or the availability of fetoscopy for early detection of congenital infection.

Biotin-labelled antigen screening test for toxoplasma IgM antibody

A method for the simple preparation of biotin-labelled toxoplasma antigen was used with avidin peroxidase in an IgM-capture enzyme linked immunosorbent assay (BAM-ELISA). Although the overall predictive value of a positive result was only 38%, its low cost and 100% sensitivity makes it a very suitable screening test. Positive results can be confirmed by an alternative assay, thus providing a more economical and effective diagnostic service than either screening all sera by a commercial test or selecting sera for IgM testing.