Letters
Infectious diseases
Volume 196 - Issue 7

Congenital toxoplasmosis over 10 years in a low-incidence population

Authors:  Jude C Jayamaha, Peter Robertson and William D Rawlinson

Med J Aust 2012; 196 (7): 443-444. || doi: 10.5694/mja11.11237
Published online: 16 April 2012
To the Editor: Vertical transmission of Toxoplasma gondii can result in significant morbidity in the fetus and newborn, although it is rare in Australia.1 Antenatal testing has shown seroprevalence of 23%-35%,2,3 which is possibly lower ...
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To the Editor: Vertical transmission of Toxoplasma gondii can result in significant morbidity in the fetus and newborn, although it is rare in Australia.1 Antenatal testing has shown seroprevalence of 23%–35%,2,3 which is possibly lower than overseas estimates. This may be because there is a higher awareness in Australian mothers of the risks of contracting toxoplasma infection from uncooked meat.

A lack of recent studies prompted us to estimate the incidence of congenital toxoplasmosis. Serological testing was performed at the South Eastern Area Laboratory Services reference serology laboratory. We reviewed T. gondii-specific antibody testing of 1684 infants (with an average age of 1 month ± 1.08 months) to investigate suspected intrauterine infection between 2000 and 2010, with multiple entries excluded. Congenital toxoplasmosis was diagnosed when an IgM assay (DiaSorin, Saluggia, Italy) and/or Platelia IgA assay (BioRad, Hercules, Calif, USA) result was positive, and a confirmatory immunofluorescence IgM assay (IFA) (bioMérieux, Lyon, France) result was positive. The same quality assurance, calibration and control methods were used over the 10-year period.

There were no diagnoses of congenital toxoplasmosis from 2000–2009, and one case was diagnosed in each of 2009 and 2010. The clinical history and findings in both cases were consistent with congenital toxoplasmosis. In the first case, there was a documented history of maternal infection confirmed by histological examination of the placenta. In the second case, there was no history of infection in pregnancy, and caesarean section was performed as the fetus developed hydrocephalus. Toxoplasma IgM was subsequently detected in maternal serum.

Over the period 2001–2009, the laboratory provided diagnostic services to obstetric facilities in south-eastern New South Wales for about 120 000 live births, giving an estimated incidence of about 0.017 per 1000 live births. This rate is lower than some earlier toxoplasmosis “prevalence at birth” estimates of 2 per 1000 infants.4 The rate is also lower than the prevalence at birth estimated at 0.23 per 1000 live births when using IgM to screen for congenital toxoplasmosis.3

In this study we used three assays to maximise test sensitivity and specificity, and we increased specificity using an IFA to reduce false-positive IgM assay results.5 Diagnosing congenital toxoplasmosis is important for prognostic and therapeutic reasons, and serodiagnosis is important, as most patients present after an acute infection. Amniotic fluid nucleic acid testing is the reference standard for diagnosis during pregnancy, but infections during pregnancy are frequently asymptomatic and so amniotic fluid testing is not contemplated. Although rare in Australia, congenital toxoplasmosis should still be considered in women and fetuses at risk of infection.

Authors

  • Jude C Jayamaha1
  • Peter Robertson1
  • William D Rawlinson2
  • 1. University of New South Wales, Sydney, NSW.
  • 2. South Eastern Area Laboratory Services, Prince of Wales Hospital, Sydney, NSW.

Correspondence: w.rawlinson@unsw.edu.au

Competing interests

No relevant disclosures.

References

View this article on Wiley Online Library

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