Anti-Toxoplasma gondii Antibodies in European Residents: A Systematic Review and Meta-Analysis of Studies Published between 2000 and 2020

Toxoplasmosis has a major impact on animal and public health. Information regarding the seroprevalence of human Toxoplasma gondii infections from a European perspective has not yet been compiled to date. Thus, the present review summarized available resident data from the period 2000–2020. The overall seroprevalence of anti-T. gondii IgG was 32.1%, with great variability between countries (n = 30). The subgroup analysis identified different pooled prevalence data depending on the geographic area (p < 0.0001), target population (p = 0.0147), and serological diagnosis assays used (p = 0.0059). A high heterogeneity (I2 = 100%, p < 0.001; Q = 3.5e+05, d.f. = 135, p < 0.001) and degree of publication bias (Egger’s test = 6.14, p < 0.001) were observed among the 134 studies considered. The occurrence of anti-T. gondii IgM, which was reported in 64.7% of studies, reached a pooled seroprevalence of 0.6%. In addition, among the eight main risk factors identified, “contact with soil”, “consumption of undercooked beef”, and “intake of unwashed vegetables” were the most significantly associated with infections. The fact that one-third of the European population has been exposed to T. gondii justifies extra efforts to harmonize surveillance systems and develop additional risk-factor analyses based on detailed source attribution assessment.


Introduction
Toxoplasma gondii is an apicomplexan intracellular parasite capable of infecting almost all homoeothermic animals, including humans [1].Toxoplasma gondii is characteristically opportunistic, and may be especially harmful in immunocompromised patients (HIVpositive, solid organ transplant recipients, etc.), but also when primary infections occur during pregnancy; congenital infections may lead to important reproductive disorders from abortions, fetal malformations, or diverse mental-retardation sequelae in children.A global disease burden estimation study [2] identified an association between the occurrence of latent toxoplasmosis and specific disease burden in 88 countries, and indeed such correlations between the presence of anti-Toxoplasma antibodies and age-standardized disability adjusted life years (DALY) explained 23% of the variability in disease burden in 29 European countries.
Comprehensive literature reviews of the status of T. gondii infections (a major zoonosis) in domestic and wild animals in Europe have been carried out [3,4]; nevertheless, regarding human populations, only one paper [5] reviewed the epidemiological situation focused on the Balkan countries (southeast Europe), and therefore no studies have been carried out from a pan-European perspective to date.Two studies analyzed the current surveillance schemes set up in Austria, France, and the USA, and highlighted the need to harmonize diagnosis and monitoring systems in most countries [6,7].
Despite the incidence of congenital toxoplasmosis in Europe (5.8 cases per 100,000 live births), which is ranked among the top causes of disease burden in EU/EEA when evaluating the disability-adjusted life years parameter [8,9], well-structured investigations concluded that most T. gondii-infections in the EU had a food-borne origin [10].In this regard, a pioneer multicenter case-control study aiming at the identification of sources of Toxoplasma-acute infections in pregnant women in Europe [11] suggested eating undercooked lamb, beef, or game meat, contact with soil, and traveling outside Europe, USA, and Canada as the major risk factors.However, remarkably, contact with cats was not identified as a risk factor.In agreement, a later meta-analysis that was focused on worldwide consumption habits [12] identified the intake of raw/undercooked beef and lamb meat as risk factors significantly associated with acute T. gondii infections in humans.In spite of this, the authors exposed the limitations due to the low number of case-control studies available.Recently, a case-control study identified consumption of meat of large game animals and poor hand hygiene as key risk factors for acute toxoplasmosis in the Netherlands [13].The complex epidemiology of T. gondii is responsible for the high number of risk factors of infection reported worldwide (reviewed in [14]).Currently, some habits and trends may have changed in the European population.In recent years, an increase in T. gondii infection cases has been clearly associated with fresh vegetable consumption [15], and it has been demonstrated that the environmental route of infection may involve a wide set of potential sources [16].Accordingly, new studies approaching the source attribution of T. gondii infections have resulted in major interest [17].
As commented above, no review paper focused on seroprevalence data on European human populations has been carried out yet; therefore, the present article aimed to systematically review and carry out a further meta-analysis of the available literature regarding two important aspects in observational studies published from 2000 to 2020: seroprevalence (IgG and IgM) data and the most suitable risk factors involved in T. gondii infections in European residents.

Materials and Methods
The present study was carried out according to the PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) [18], and the PRISMA checklist is available in Supplementary Table S1.The performance workflow followed in the present study is shown in Figure 1.
Literature published between January 2000 and December 2020 was searched in electronic databases (PubMed, Science Direct, Scopus, WoS and SCIelo) using medical subject headings (MeSH) terms (Toxoplasma gondii, toxoplasmosis, seroprevalence, human, Europe); selection (eligibility criteria: serosurveys [excluding review papers; case-control studies were only considered for the risk factors study/analyses], years 2000 to 2020, continental Europe, any language); and further critical review and a meta-analysis were carried out as previously proposed [19].Initially, abstracts were revised for study screening and further data extraction; the whole process was carried out by two investigators.Additional references cited in the bibliography of the evaluated papers were considered eligible.Papers in languages other than English (to note: Croatian, French, German, Icelandic, Italian, Polish, Portuguese, Serbian, Spanish, and Russian) were taken into consideration.From each eligible study dealing with anti-T.gondii IgG and IgM data or risk fact analysis, detailed information on study area, year/data of sampling, target populati diagnostic method, sample size, and number of positive samples was collected.In ad tion, data on significant risk factor conditions (odds ratio, relative risk, and significan were gathered in those specific studies (Supplementary Table S2).Regarding data ana sis, for the evaluation of pooled estimates (detection rates reported in each study), a stricted maximum likelihood method with a random effects model was used [20].Stu bias and heterogeneity at the study level were calculated using Egger's test, and Cochra Q test and inverse variance index (I 2 ), respectively [20][21][22].Alpha was set at 0.05.

Seroprevalence of Anti-T. gondii IgG in European Residents
A total of 136 published studies on T. gondii IgG seroprevalence in humans in Euro published between 2000 and 2020, with 30 countries represented, were eligible and cluded in this meta-analysis (Table 1).Europe was divided into 4 regions: North, wit countries (Estonia, Finland, Iceland, Ireland, Norway, Sweden, and United Kingdom) a 51 published studies; West, with 6 countries (Austria, Belgium, France, Germany, Neth lands, and Switzerland) and 47 studies; East, with 6 countries (Czech Republic, Hunga Poland, Romania, Russia, and Slovakia) and 18 publications; and finally South, with countries (Albania, Bosnia and Herzegovina, Croatia, Cyprus, Greece, Italy, North Ma donia, Portugal, Serbia, Slovenia, and Spain) and 20 studies.For the analysis of IgG se prevalence, the samples were obtained from the following: general population (n = studies), pregnant women or women of childbearing age (n = 58), and others (n = 47), a the diagnostic methods that were used were based on commercial tests (n = 101 studie in-house tests (n = 15), and a combination of both (n = 8) (Table 2).From each eligible study dealing with anti-T.gondii IgG and IgM data or risk factors analysis, detailed information on study area, year/data of sampling, target population, diagnostic method, sample size, and number of positive samples was collected.In addition, data on significant risk factor conditions (odds ratio, relative risk, and significance) were gathered in those specific studies (Supplementary Table S2).Regarding data analysis, for the evaluation of pooled estimates (detection rates reported in each study), a restricted maximum likelihood method with a random effects model was used [20].Study bias and heterogeneity at the study level were calculated using Egger's test, and Cochran's Q test and inverse variance index (I 2 ), respectively [20][21][22].Alpha was set at 0.05.

Seroprevalence of Anti-T. gondii IgG in European Residents
A total of 136 published studies on T. gondii IgG seroprevalence in humans in Europe, published between 2000 and 2020, with 30 countries represented, were eligible and included in this meta-analysis (Table 1).Europe was divided into 4 regions: North, with 7 countries (Estonia, Finland, Iceland, Ireland, Norway, Sweden, and United Kingdom) and 51 published studies; West, with 6 countries (Austria, Belgium, France, Germany, Netherlands, and Switzerland) and 47 studies; East, with 6 countries (Czech Republic, Hungary, Poland, Romania, Russia, and Slovakia) and 18 publications; and finally South, with 11 countries (Albania, Bosnia and Herzegovina, Croatia, Cyprus, Greece, Italy, North Macedonia, Portugal, Serbia, Slovenia, and Spain) and 20 studies.For the analysis of IgG seroprevalence, the samples were obtained from the following: general population (n = 38 studies), pregnant women or women of childbearing age (n = 58), and others (n = 47), and the diagnostic methods that were used were based on commercial tests (n = 101 studies), in-house tests (n = 15), and a combination of both (n = 8) (Table 2).for pregnant women or women of childbearing age, and 31.1% (95% CI 29.0-33.1)for other groups of the population considered to be people at higher risk (e.g., health care workers, abattoir workers, farmers, hospital patients, etc.).Statistically significant differences were observed for seroprevalence in the general population compared to that of pregnant women/women of childbearing age (p = 0.011).
The frequencies obtained of T. gondii IgG antibodies for the type of diagnostic method used were 30.2% (95% CI 28.1-32.3),40.1% (95% CI 35.4-44.8),and 43.2% (95% CI 35.4-51.0)for commercial, in-house, and a combination of both, respectively, and a statistically significant difference (p = 0.011) was observed when commercial and in-house methods were compared.Supplementary Figures S1 and S2 present the forest plot of the seroprevalence of IgG antibodies by country and funnel plots of IgG seroprevalence by the variables analyzed (region, type of population, and analytical methods), respectively.A high heterogeneity (I 2 = 100%, p < 0.001; Q = 3.5 × 10 5 (d.f.= 135), p < 0.001) and degree of publication bias (Egger's test = 6.14, p < 0.001) were observed among the 134 studies considered.
The frequencies obtained of T. gondii IgG antibodies for the type of diagnostic method used were 30.2% (95% CI 28.1-32.3),40.1% (95% CI 35.4-44.8),and 43.2% (95% CI 35.4-51.0)for commercial, in-house, and a combination of both, respectively, and a statistically significant difference (p = 0.011) was observed when commercial and in-house methods were compared.Supplementary Figures S1 and S2 present the forest plot of the seroprevalence of IgG antibodies by country and funnel plots of IgG seroprevalence by the variables analyzed (region, type of population, and analytical methods), respectively.A high heterogeneity (I 2 = 100%, p < 0.001; Q = 3.5 × 10 5 (d.f.= 135), p < 0.001) and degree of publication bias (Egger's test = 6.14, p < 0.001) were observed among the 134 studies considered.

Identification of Risk Factors
Thirty studies reported data from 23 countries on risk factors for T. gondii infection (Supplementary Table S2).Among those, one study was multicentric, involving five countries (Belgium, Denmark, Italy, Switzerland, and Norway) from the North, South, and West areas [11], and two studies were undertaken in two East countries (Czech Republic and Slovakia) [168], and in three North countries (Sweden, Estonia, and Iceland) [23].Among such heterogeneous studies, eight main risk factors were reported in Europe (Figure 3); within those, the most frequently investigated were "contact with cats" (63% [19/30] of studies), "consumption of raw (or undercooked) meat" without specification of the animal species of origin (60% [18/30]), "specific occupation of risk and working with animals" (47% [14/30]), and "contact with soil" (43% [13/30]); nevertheless, within each risk factor category and attending to the frequency/proportion of studies presenting associated statistical significance, "contact with soil" (9/13 [70%] studies), "intake of undercooked beef" (4/6 [66%] studies), and "intake of unwashed vegetables and fruits" (5/8 [63%] studies) stood out as demonstrated main facts associated with seroconversion and infections in European residents.

Identification of Risk Factors
Thirty studies reported data from 23 countries on risk factors for T. gondii infe (Supplementary Table S2).Among those, one study was multicentric, involving five tries (Belgium, Denmark, Italy, Switzerland, and Norway) from the North, South West areas [11], and two studies were undertaken in two East countries (Czech Rep and Slovakia) [168], and in three North countries (Sweden, Estonia, and Iceland) Among such heterogeneous studies, eight main risk factors were reported in Europe ure 3); within those, the most frequently investigated were "contact with cats" [19/30] of studies), "consumption of raw (or undercooked) meat" without specificati the animal species of origin (60% [18/30]), "specific occupation of risk and working animals" (47% [14/30]), and "contact with soil" (43% [13/30]); nevertheless, within risk factor category and attending to the frequency/proportion of studies presenting ciated statistical significance, "contact with soil" (9/13 [70%] studies), "intake of u cooked beef" (4/6 [66%] studies), and "intake of unwashed vegetables and fruits" [63%] studies) stood out as demonstrated main facts associated with seroconversion infections in European residents.S2.

Discussion
The present study aimed at summarizing the anti-Toxoplasma IgG and IgM sero alence data of human populations residing in Europe contained in studies publishe tween 2000 and 2020.Previous reviews [169][170][171][172] accomplished this task from a g point of view.In general, remarkable differences in the seroprevalence against T. gon different areas and continents were reported, in agreement with the fact that major r of transmission differ in distinct human contexts involving different cultures, soci nomic development, and culinary habits.
The present review evidences a pooled overall seroprevalence in European resi (IgG: 32.1%; IgM: 0.6%) that is in the line with other international studies and are similar socioeconomic status (and habits).Comparable studies in the general popu of the USA between 2011 and 2014 estimated that seroprevalence reached a low le 11.14% (95% CI: 9.88-12.51)for IgG antibodies [173].Indeed, an overall IgG serop lence of 17.5% in USA/Canada has been reported (reviewed in [171]).
Despite being beyond the scope of the present review, a more specific systema view [174] focused on the global prevalence of latent toxoplasmosis in pregnant wo The authors reported 31.2%seropositivity in European pregnant women (from 19 2019), which is in agreement with data reported here (e.g., 28.3% in the present rev Nevertheless, current occurrences (e.g., last 5 years) may be lower, since the epidemi  S2.

Discussion
The present study aimed at summarizing the anti-Toxoplasma IgG and IgM seroprevalence data of human populations residing in Europe contained in studies published between 2000 and 2020.Previous reviews [169][170][171][172] accomplished this task from a global point of view.In general, remarkable differences in the seroprevalence against T. gondii in different areas and continents were reported, in agreement with the fact that major routes of transmission differ in distinct human contexts involving different cultures, socioeconomic development, and culinary habits.
The present review evidences a pooled overall seroprevalence in European residents (IgG: 32.1%; IgM: 0.6%) that is in the line with other international studies and areas of similar socioeconomic status (and habits).Comparable studies in the general population of the USA between 2011 and 2014 estimated that seroprevalence reached a low level of 11.14% (95% CI: 9.88-12.51)for IgG antibodies [173].Indeed, an overall IgG seroprevalence of 17.5% in USA/Canada has been reported (reviewed in [171]).
Despite being beyond the scope of the present review, a more specific systematic review [174] focused on the global prevalence of latent toxoplasmosis in pregnant women.The authors reported 31.2%seropositivity in European pregnant women (from 1988 to 2019), which is in agreement with data reported here (e.g., 28.3% in the present review).Nevertheless, current occurrences (e.g., last 5 years) may be lower, since the epidemiological situation has clearly evolved with the evidence provided by several long-term observational studies.Two of these deserve attention: a French survey focused on pregnant women reported a decrease in IgG prevalence from 55.0% in 1995 to 33.7% in 2016 [175], and another comprehensive investigation from Austria reported a yearly decline in IgG seroprevalence of 0.56% in the time period 1995-2006, and a 1.20% annual decline from 2006 to 2012; in sum, IgG seroprevalence decreased from 43.3% in 1995 to 31.5% in 2012 [43].Both countries have a well-established national surveillance system [176].As a consequence, national (local/regional) longitudinal studies in different population strata (e.g., health workers, children, etc.) are clearly necessary to assess the true expected decreasing trends in the remaining European countries.
One limitation of the present review is that the mean age of female participants from each study was unknown.This demographic nuance may create the illusion of deflated prevalence rates among pregnant women in specific areas.Therefore, readjustments of the prevalence to standard ages through mathematical procedures would have been desirable to overcome such a bias [177,178].
As usually reported, the presence of IgM is investigated as an indicator of recent Toxoplasma infection, which is the rationale for the majority (66%) of surveys targeting pregnant women or newborn children (Table 3).The seroprevalence values observed in European regions (range: 0.1-1.1%)are in accord with other areas of similar sociodemographic level, such as the USA (1.16% (95% CI: 0.94-1.42)[173].Despite IgM figures being of epidemiological interest, additional extra effort should be made in many countries to estimate the incidence of clinical toxoplasmosis and its further report (e.g., congenital toxoplasmosis) [8].
Detailed and harmonized data compilation results are of great interest for comparisons among areas, but especially when comprehensive data analyses (e.g., association by logistic regression models) are desired [2,179,180].In this regard, the lack of harmonization especially among the available serological diagnostic methods [181] can hinder the possibilities of making comparisons between studies; this is a fact that is frequently observed in other meta-analyses, in which the heterogeneity values observed used to be high (>75%) [20,174].
Despite the remarkable degree of heterogeneity observed, the frequency of exposure to T. gondii is also high and widespread; therefore, unraveling the most common route of infection is highly desirable to design appropriate intervention strategies.
Currently, the relative importance of meat-borne vs. oocyst-driven transmission of T. gondii is little known.A review of the literature indicates that 30-60% of infections could be attributed to meat as the infection source, while 6-17% could be attributed to contact with soil or other environmental matrices containing oocysts [11,15,182].Therefore, studies aiming to unravel what the main sources of infection are for European residents are of major interest [14,16].
Systematically compiling the information is key for the identification of patterns related to toxoplasmosis outbreaks [15,172,183].Whether the severity of clinical infections in humans is associated with one of such routes is not known; however, in laboratory animals, oocysts, as a source of infection, cause more severe clinical disease [172].A worldwide systematic review of T. gondii outbreaks [183] selected 38 studies reporting details regarding epidemiological data and dynamic of infections.Some findings deserve attention, notably, a large number of individuals were affected when oocysts were the suspected or confirmed source of infection, and a broader and prolonged appearance of new cases occurred via such a source when compared to tissue cysts.There is limited information regarding Europe, where very few outbreaks have been observed, which were associated with ingestion of unpasteurized milk [184] and undercooked meat [185][186][187].
More recently, additional data on the patterns of transmission and source of infection in global outbreaks of human toxoplasmosis have been reported [15]; authors suggested that transmission routes presented variations by decade.For example, in the 1960s and 1990s, ingestion of cysts in meat and meat products were considered the main sources of infection; in the 1980s, milk contaminated with tachyzoites; in the 2000s, the outbreaks were more related to the presence of oocysts in water, sand, and soil; and after 2010, due to oocysts in raw fruits and vegetables.Therefore, additional studies on the source attribution that aim to identify the true source of infection are warranted [17].
Despite very few toxoplasmosis outbreaks having been reported in Europe [183], exposure to the parasite is frequent, and major risk factors have been identified based on its statistical association with infections.Knowledge of risk factors related to diet, hygiene practices, and lifestyle will help to target prevention efforts.In the present review (Supplementary Table S2), the eight worldwide main risk factors related to the meat-borne and the environmental routes were considered [14].Among the 30 studies reporting such information in the last 20 years in Europe, three risk factors ("contact with soil", "consumption of undercooked beef", and "intake of unwashed vegetables") stood out as the most frequently associated to seroconversion in people.
Nevertheless, in the present review, consumption of other products of animal origin (raw eggs, and unpasteurized milk) was proven to be a non-significant risk factor, unlike in other areas such as the USA where drinking unpasteurized goat's milk was a risk factor (OR = 5.09; 95% CI: 1.45-17.80)[191] and has been recognized as a cause of outbreaks [183].
Among the risk factors related to the environmental route [192], "contact with soil" and "intake of unwashed vegetables and fruits" were the most frequently identified (70% and 63% of studies, respectively) in the present review; both are related to T. gondii oocysts contamination [16] that is the product of sexual multiplication of the parasite in the gut of felines, which is quite resistant to environmental harmful conditions; a single sporulated oocyst is capable of producing the infection [1].In European studies prior to 2000, "frequent consumption of raw vegetables outside the home" (OR = 3.1; 95% CI: 1.2-7.7)[188] and "eating unwashed raw vegetables or fruits" (OR = 2.4; 95% CI: 1.1-5.6)[190] had also been identified as risk factors.Also, in the USA [191], "eating raw oysters, clams, or mussels" (OR = 2.22; 95% CI, 1.07-4.61;AR, 16%) was significant in a separate model among persons asked this question, reinforcing the importance of environmental routes for human infections as demonstrated during outbreaks investigations [15].In this regard, the remarkable frequency of detection of T. gondii oocysts in fresh produce, mollusk bivalves, and water bodies worldwide [16] increases research interest to specifically investigate the relative importance of the environmental route vs. the meat-borne route.
Among other recognized risk factors, "contact with cats" was associated with T. gondii infection in 5 of the 19 studies (Supplementary Table S2), where the variable was considered despite the well-established low frequency of cats shedding oocysts at a given time [22].Such a risk factor had not been considered in previous studies carried out in Europe [189]; however, in the USA, "having three or more kittens" was significantly associated with infections (OR = 27.89;95% CI: 5.72-135.86)[191].Despite the epidemiological importance of cats in T. gondii transmission, contact with cats was also not the predominant risk factor for infection in studies carried out in other parts of the world [12,14]; it was not even identified in the first European multicenter study focused on pregnant women residing in six cities of five countries (Belgium, Denmark, Italy, Norway, and Switzerland) [11].Other risk factors like "gardening" and "traveling out of Europe or the USA" have been recognized as significant [189][190][191].Finally, the same authors [173] proposed some sociodemographic risk factors via a full logistic regression model (e.g., ethnic origin, place of birth, crowding, etc.); similar studies have been carried out for European populations (e.g., [154]).
As observed in the present review (Supplementary Table S2) for Europe, and in agreement with studies carried out in other geographical scenarios, most investigations focused on recent/primary infections in pregnant women.In a recent review [14] considering 187 case-control, cohort, and cross-sectional studies conducted worldwide between 1983 and 2016, the authors showed a long list of potential risk factors and highlighted the association of T. gondii sporadic infections with a wide range of environmental factors, along with those related to food habits.The authors declared that the main limitation for making inferences from the data (data interpretation) were the broad definition of exposures and the use of serological methods for the case definition.In this very same context, a major limitation arises; most of the worldwide studies reported risk factors related to T. gondii infections without taking the moment of infection into account (e.g., based upon IgG seropositivity) [13].Indeed, new studies are necessary to clarify the major sources of infections for the human population in the EU.In this regard, a recent paper in the Netherlands [13] identified the importance of hand hygiene, and the need for detailed enquiries (including risk assessment) with specific meat types.
Despite the present review's focus on risk factors related to both meat-borne and environmental route-derived infections, further studies also addressing neglected risk factors (e.g., injuries caused by animals, sexual contact, etc.) [168,[193][194][195] would be of interest.
The interest of regional-specific analyses to identify specific risk factors (e.g., casecontrol studies with country-specific products [13]) and the implementation of tools like quantitative microbial risk assessment (QMRA) methods [196] will clarify the current epidemiological scenario.Therefore, an integrative analysis from a One Health point of view will be of major interest to unravel and quantify the sources of T. gondii infections for human populations in Europe, which, by contrast, are subject to rapid change.
In summary, several needs are identified: source attributions and updated risk factors studies are missing in most countries under situations of rapid changes in food preferences and trends.A brief summary of each of the elements is presented below.
(a) There is a lack of seroprevalence data from several countries (e.g., Baltic states).(b) Apparent regional differences may be due to the absence of harmonized data (e.g., type of target population), but also due to differences in a country's culinary customs and sociodemographic development index.(c) The high heterogeneity observed indicates the lack of harmonization of approaches (e.g., diagnostic methods) for T. gondii seroprevalence investigations in Europe.Given the high heterogeneity observed in the present study, it is clear that surveillance systems should first be implemented, and then harmonized in European countries [6,7,176].
(d) Development of up-to-date risk assessment (local/regional) studies taking into consideration particular trends are needed.
The overall results show that a noticeable segment of the European population (onethird) harbors anti-Toxoplasma IgG antibodies.Therefore, exposure to T. gondii seems to be frequent, and should be considered especially among people at risk.However, under the view of scattered and fragmented available data, a harmonized system for Toxoplasma infection surveillance in European countries is missing.In addition, extra efforts should be made to implement updated risk-factor analyses focusing on detailed source attribution in such a dynamic and evolving society, since culinary customs (and preferences) are rapidly changing.

Conclusions
Therefore, exposure to T. gondii seems to be frequent among European residents, and should be considered especially among vulnerable people.However, under the view of the scattered and fragmented data available, a harmonized system for Toxoplasma infection surveillance should be implemented in Europe, in order to better estimate the epidemiological scenario regarding T. gondii infection and its potential clinical toxoplasmosis (e.g., congenital toxoplasmosis).In addition, extra effort should be made to implement updated local risk-factor analyses focusing on detailed source attribution in such a dynamic and evolving society, since culinary customs (and preferences) are rapidly changing.

Figure 1 .
Figure 1.Flowchart describing the study design process.Description of the study search and sel tion for publications related to (A) seroprevalence of IgG and IgM anti-T.gondii antibodies, and risk factors analyses.(*) A secondary search was carried out based on references included in artic examined for eligibility.

Figure 1 .
Figure 1.Flowchart describing the study design process.Description of the study search and selection for publications related to (A) seroprevalence of IgG and IgM anti-T.gondii antibodies, and (B) risk factors analyses.(*) A secondary search was carried out based on references included in articles examined for eligibility.

Figure 3 .
Figure 3. Summary of the risk factors identified for T. gondii infection in human populations re in Europe.Each bar indicates the number of studies that considered such potential risk facto the numbers of them resulting in a statistical association were evaluated with odds ratio or re risk.Brackets indicate the proportions of studies considering such factors as statistically sign (p < 0.05).Raw data are presented in Supplementary TableS2.

Figure 3 .
Figure 3. Summary of the risk factors identified for T. gondii infection in human populations residing in Europe.Each bar indicates the number of studies that considered such potential risk factors and the numbers of them resulting in a statistical association were evaluated with odds ratio or relative risk.Brackets indicate the proportions of studies considering such factors as statistically significant (p < 0.05).Raw data are presented in Supplementary TableS2.

Table 1 .
Summary of selected studies on seroprevalence of anti-T.gondii antibodies (IgG) in European residents published between 2000 and 2020.
ELFA: enzyme-linked fluorescence assay; IFAT: immunofluorescent antibody test; MEIA: microparticle enzyme immunoassay; SF: Sabin-Feldman dye test.* Studies included here in which analytical methods were not reported (NR) were selected because of the interest of the whole publication in the specific geographical context (e.g., representativeness).

Table 3 .
Summary of studies reporting anti-T.gondii antibodies (IgM) in European residents published between 2000 and 2020.
NR: not reported; CM: commercial system/kit; CFT: complement fixation test; CMIA: chemiluminescent microparticle immunoassay; ISAGA: immunosorbent agglutination assay; ELFA: enzyme-linked fluorescence assay; ELISA: enzyme-linked immunosorbent assay; MEIA: microparticle enzyme immunoassay.* Studies included here in which analytical methods were not reported (NR) were selected because of the interest of the whole publication in the specific geographical context (e.g., representativeness).