As shown in Fig. 1, more than two-thirds of the study group were in the neonatal group of patients aged until 28 days. The median age was 10 days, while the average age was 31 days. The age distribution may be due to the diagnostic capabilities of CT, including prenatal serological screening for toxoplasmosis, which is imposed by legal regulations in Poland24. In addition, in the group of mothers suspected of having active toxoplasmosis during pregnancy, amniocentesis can be performed to determine T. gondii DNA material based on PCR, which has specificity of 100% and sensitivity of 90%31. Furthermore, tests such as prenatal and postnatal ultrasound can highlight characteristic lesions such as calcifications in the brain10. Modern diagnostic methods result in the early detection of the disease and the possibility of quick implementation of necessary treatment. CT diagnosis can also take place in the following months of life, due to the existence of a spectrum of symptom severity, depending on the stage of pregnancy at which the foetus was infected3,4.
Between 2007 and 2021, there was an average of about 380,000 live births per year in Poland. The incidence of CT in the years 2007–2021 was 2.6 per 10,000 live births. Compared to the previously available data on the Polish population, this is a relatively low rate. Studies from the Poznan region that focused on the years 1998–2000 estimated the incidence of CT at 10.8 per 10,000. Based on the studies conducted in Lodz in 2004–2012 which assessed the serological status of pregnant women, the extrapolation of data set the incidence of CT at 18 per 10,000. None of the studies assessed the incidence of CT at a nationwide level. An additional factor overestimating the rates may have been the fact that the studies were limited to referral centres, which may have aggregated cases of complicated pregnancies, such as those with coexisting toxoplasmosis. In addition, only the first study assessed CT directly, but it was done in the last century, while the second study only extrapolated the serological results of pregnant women to the expected incidence of CT among newborns26,27.
A comparison on a global scale indicates that the incidence of the disease in Poland is lower than the assumed global average of 15 cases per 10,000 live births15. An analysis of detailed data from individual countries shows that the incidence of CT at 2.6 per 10,000 live births is similar to that in other European countries, such as Austria (1 per 10,000), Denmark (2.1 per 10,000), and France (2.9 per 10,000)16,17,18. These results are also similar to available data from the US (1 per 10,000)21. It should be noted that data from the physician-reported case registry in Poland indicate a lower incidence rate than it has been estimated in this study32. The official European Centre for Disease Prevention and Control (ECDC) report on CT in 2019 indicates the incidence of 0.51 per 10,000 live births in Europe. When comparing these data with available studies from individual countries, including the study presented here, the information provided by the ECDC may be underestimated, for example, due to international reporting issues33. There is some contrast between these results and data from countries such as Morocco (3.9–8 per 10,000), Brazil (4–23 per 10,000), and Panama (18 per 10,000), where the incidence is significantly higher7,19,20,21,23. Differences in CT incidence across regions may be due to factors such as access to medical care, socioeconomic conditions, level of public awareness of TORCH infections, national public health standards, and hygienic conditions. The data for Poland puts this country among other developed Western countries, which may be due to both broad access to modern diagnostic and treatment methods, educational programs and legal solutions to reduce CT infections24. The results of a study from China on the causes of infant hospitalizations in the years 2015–2020 showed a very low incidence of CT, as only 0.07 per 10,000 hospitalized children under 1 year of age (5 cases) were reported. These data determined the results only for a selected group of tertiary hospitals in China22.
As presented in Fig. 2, the incidence of CT in Poland in the years 2007–2021 fluctuated, with the highest incidence in 2010 and the lowest one in 2014. As we can observe in Fig. 2, lower incidence values were registered between 2011 and 2015, relative to other years of the study period. Globally, a decreasing trend in seropositivity against T. gondii is observed, but this does not always reflect a direct decrease in CT incidence. It is believed that the influence of a number of factors, such as demographic structure, cyclical changes in the percentage of the population susceptible to infection, and dynamically changing legal and socio-health conditions may result in a sinusoidal trend in CT incidence in individual societies over many years34.
The study analysed comorbidities. In the study group, the most common concomitant diagnoses were those described in the literature as occurring in the course of CT, such as malformations and deformations (13. 3% of all patients), neonatal jaundice (11.9%), prematurity and low birth weight (5.8%) and diseases of the nervous system (5.2%). The above symptoms and diseases correspond to those typically seen in CT. The most characteristic triad of symptoms are chorioretinitis, intracranial calcifications, and hydrocephalus, but prematurity, spontaneous abortion, stillbirth, liver or spleen enlargement, jaundice, fever, microcephaly, hearing abnormalities, pneumonia, myocarditis, and many others can also be observed2,8,9,10. Attention is also drawn to the frequent congenital co-infection with CMV (11.3%), which could have exacerbated the neurological changes caused by both pathogens.
During the study, 8 hospital deaths of CT patients occurred (0.5% of the whole group)—congenital toxoplasmosis was identified as the primary or secondary cause of death in 6 of the 8 deaths. In the remaining cases, cardiovascular diseases were the cause of death in one and respiratory diseases in the second case. Given the possibility of developmental abnormalities of various organs and various severity in CT, these deaths may also have been indirectly related to CT3,4. This is a relatively low figure. Another study conducted in the years 1974–2007, where causes of infant deaths in Japan were analysed, found two neonatal deaths due to CT (0.001% of all neonatal deaths)35. However, the mortality rate may be underestimated due to miscarriages early in pregnancy, which can occur during intrauterine infection.
No significant gender differences were observed in the study with regard to the incidence, which is consistent with the ECDC report on CT in Europe, where the female-to-male ratio was 1:133.
Based on data for Poland from 2007 to 2021, there were no significant differences between the incidence of CT according to the place of residence (urban versus rural areas). Although based on data from a single centre in the capital city, rural residence was found to be an independent risk factor for toxoplasmosis in pregnant women in Poland, this does not translate into a higher incidence of CT in infants from rural areas25. The lack of differences between urban and rural areas may also be due to the standards of care applied throughout the country, which are defined by legal regulations. These standards specify, in addition to the methods of early detection and implementation of effective treatment, appropriate education of pregnant patients on the potential risks and ways of infection with T. gondii24. Improvement of access to medical care in Poland, as well as availability of educational materials and recommendations on the Internet may lead to a reduction in the differences between incidence in urban and rural populations, despite greater environmental exposure.
Despite its advantages, the presented study also has its limitations, mainly due to its retrospective nature. In the course of the analysis, we did not verify the findings on the basis of which CT was diagnosed. We assume that the diagnosis is based on the most current, widely used diagnostic criteria for this disease entity. The incidence of CT in Poland was assessed on the basis of first-time hospitalizations for the disease, due to the need for specialized testing and implementation of treatment when the disease occurs in newborns. In addition, the date of hospitalization after birth may inaccurately represent the actual date of diagnosis, due to the possibility of prenatal detection. Due to these limitations, the incidence by year may have been represented inaccurately, but the long observation period and large sample size of the data obtained from the national registry may minimize this imprecision.