Long-term Ocular Outcomes in Congenital Toxoplasmosis Treated Perinatally.

BACKGROUND: Congenital toxoplasmosis (CT) can be accompanied by serious organ manifestations, particularly retinochoroiditis, and may occur throughout life. We aimed to monitor long-term ocular prognosis in a large French cohort of patients with CT and its changes over time in the context of mandatory prenatal screening (since 1992) and incidence decrease since 2008. METHODS: Patients with CT diagnosed between 1987 and 2021 were prospectively included and followed for up to 35 years. The effect of the period of conception on the risk of first retinochoroiditis has been tested using a flexible extension of the Cox model. Incidence rates of retinochoroiditis were estimated. RESULTS: A total of 646 infected live born children were followed for a median of 12 years (range, 0.5-35); 187 patients (29%) had at least 1 ocular lesion (first at a median age of 5 years; range, 0-26 years) with peaks at 7 and 12 years. Early maternal infection and the presence of nonocular signs at birth were associated with a higher risk of retinochoroiditis, whereas delayed diagnosis of CT (after birth versus before or at birth) was associated with a lower risk (13% decrease for each additional month after birth; P = .01). A period effect for the risk of developing retinochoroiditis in patients born after 2008 was not detected. CONCLUSIONS: Despite prenatal screening and prolonged perinatal treatment, retinochoroiditis is not a rare event in French patients with CT and can occur well into adulthood, with peak incidences at 7 and 12 years of age. It rarely causes severe damage but warrants regular follow-up into adulthood.

The incidence, presenting clinical findings and treatment patterns of Birdshot Retinochoroiditis in a high-prevalence region: findings from Northern Ireland, England and Wales.

BACKGROUND: Birdshot Retinochoroiditis (BSRC) is a rare, chronic posterior uveitis that is strongly associated with HLA-A*29.2 positivity. To date, no robust incidence studies of BSRC have been undertaken. We present the first epidemiological study of BSRC in a high-prevalence region. METHODS: In collaboration with the British Ophthalmological Surveillance Unit, all new cases of BSRC between May 2017 and June 2019 were prospectively collected. Presenting demographics, symptoms, signs and treatment modalities were collected. A follow-up questionnaire twelve months later was also sent. RESULTS: Thirty-seven confirmed cases meeting the reporting criteria were identified. Twenty-three cases had both baseline and follow-up data. The total population incidence of BSRC was 0.035 cases per 100,000 person-years [95% CI 0.025-0.048 cases per 100 000 people]. 97.3% were HLA-A*29 positive. The median age was 46 years, with females making up 78% of patients. There were no significant differences in the latitudinal incidence of BSRC. At presentation, floaters were the most common symptom. Optic disc swelling was the most common sign. Mean presenting visual acuity was independent of symptom duration. Combined systemic corticosteroids and immunomodulatory therapy were the most common treatments at baseline and follow-up. Intravitreal steroids were equally popular at follow-up. CONCLUSIONS: This study provides the first nationwide estimate of the incidence of BSRC in a high-prevalence region. Cases were more common in females, with a broad range of presentation ages. No significant latitudinal effect of incidence was identified. Systemic therapy with steroids and IMT remain the most common treatments.

Rate of recurrence of toxoplasmosis retinochoroiditis at a tertiary eye centre in Auckland.

AIM: Our aim was to examine rate of recurrence of toxoplasmosis retinochoroiditis and risk factors for recurrence. No New Zealand epidemiological data on recurrence rates of toxoplasmosis retinochoroiditis have been previously published. METHODS: Retrospective chart review of all patients with toxoplasmosis retinochoroiditis presented to Auckland District Health Board Department of Ophthalmology between 2006-2019. RESULTS: One hundred and twenty-six eyes of 115 patients were included with a median age at initial diagnosis of 36.7 years (IQR 23.7-53.8). Fifty-nine patients were female (51.3%), and 16 patients (13.9%) were immunosuppressed. Twenty-six of the 86 patients tested (30.2%) were IgM positive at presentation. Mean follow-up was 6.1 years and 73 recurrences occurred during the follow-up period in 36 patients (31.3%). Treatment was initiated in 87.4% of cases, with oral cotrimoxazole or clindamycin the most common options. Recurrence occurred in 14.8% in the first year (95% CI 10.3%-21.0%), and the risk of recurrence was increased 2x for every previously documented recurrence (HR 2.00; p<0.001). There was no statistically significant increased risk of recurrence with age, IgM positivity, immunosuppression or macular involvement. CONCLUSIONS: Toxoplasmosis retinochoroiditis had a 14.8% risk of recurrence in the first year, with each previous recurrence increasing the risk by two-times.

Prevalence of Toxoplasmic Retinochoroiditis in an Australian Adult Population: A Community-Based Study.

PURPOSE: Toxoplasmic retinochoroiditis is the most common clinical manifestation of an infection with the protozoan parasite, Toxoplasma gondii. Up to 50% of the human population is estimated to be infected with T. gondii; however, the epidemiology of toxoplasmic retinochoroiditis has not been widely reported. We sought to estimate the prevalence of toxoplasmic retinochoroiditis in Australia using data that were collected as part of the Busselton Healthy Ageing Study. DESIGN: Cross-sectional, community-based, prospective cohort study. PARTICIPANTS: 5020 Australian adults (2264 men and 2756 women; age range, 45-69 years, and median age, 58 years). METHODS: Retinal color photographs, centered on the optic disc and macula, were captured using a digital retinal camera after the dilation of the pupils. Three uveitis-subspecialized ophthalmologists assessed each pigmented retinal lesion, and complete concordance of opinion was required to assign a toxoplasmic etiology. Serum T. gondii immunoglobulin (Ig)G levels were measured for those participants with retinal lesions judged to be toxoplasmic retinochoroiditis. MAIN OUTCOME MEASURES: Prevalence of toxoplasmic retinochoroiditis. RESULTS: Eight participants (0.16%) had retinal lesions that were considered to have the characteristic appearance of toxoplasmic retinochoroiditis, plus detectable serum T. gondii IgG, consistent with the diagnosis of toxoplasmic retinochoroiditis. On the assumption that 23.81% of retinal lesions occur at the posterior pole, as reported in a community-based survey conducted in Brazil (Sci Rep. 2021;11:3420), the prevalence of toxoplasmic retinochoroiditis was estimated to be 0.67% or 1 per 149 persons. CONCLUSIONS: Toxoplasmic retinochoroiditis is common in Australian adults. Efforts to quantify and address risk factors for human infection with T. gondii are justified.

A genotype-phenotype correlation matrix for ABCA4 disease based on long-term prognostic outcomes.

BackgroundMore than 1500 variants in the ATP-binding cassette, sub-family A, member 4 (ABCA4), locus underlie a heterogeneous spectrum of retinal disorders ranging from aggressive childhood-onset chorioretinopathy to milder late-onset macular disease. Genotype-phenotype correlation studies have been limited in clinical applicability as patient cohorts are typically small and seldom capture the full natural history of individual genotypes. To overcome these limitations, we constructed a genotype-phenotype correlation matrix that provides quantifiable probabilities of long-term disease outcomes associated with specific ABCA4 genotypes from a large, age-restricted patient cohort.MethodsThe study included 112 unrelated patients at least 50 years of age in whom 2 pathogenic variants were identified after sequencing of the ABCA4 locus. Clinical characterization was performed using the results of best corrected visual acuity, retinal imaging, and full-field electroretinogram testing.ResultsFour distinct prognostic groups were defined according to the spatial severity of disease features across the fundus. Recurring genotypes were observed in milder prognoses, including a newly defined class of rare hypomorphic alleles. PVS1 (predicted null) variants were enriched in the most severe prognoses; however, missense variants were present in a larger-than-expected fraction of these patients. Analysis of allele combinations and their respective prognostic severity showed that certain variants, such as p.(Gly1961Glu), and both rare and frequent hypomorphic alleles, were "clinically dominant" with respect to patient phenotypes irrespective of the allele in trans.ConclusionThese results provide much-needed structure to the complex genetic and clinical landscape of ABCA4 disease and add a tool to the clinical repertoire to quantitatively assess individual genotype-specific prognoses in patients.FUNDINGNational Eye Institute, NIH, grants R01 EY028203, R01 EY028954, R01 EY029315, P30 19007 (Core Grant for Vision Research); the Foundation Fighting Blindness USA, grant no. PPA-1218-0751-COLU; and Research to Prevent Blindness.

Incidence of chorioretinitis and endophthalmitis in hospitalized patients with fungemia.

AIM/PURPOSE: Bloodstream candida infections can seed the eye via hematogenous spread and result in chorioretinitis or endophthalmitis. If undetected and untreated, this can result in permanent vision loss. Past studies evaluating incidence of ocular candidiasis among hospitalized patients with positive fungal blood cultures have demonstrated variable rates of occurrence, but recent studies have generally shown a lower incidence than was reported several decades ago. Given low rates of occurrence, the utility of screening patients with dilated fundus exams has been called into question. The primary aim of this investigation is to identify the rate of chorioretinitis and endophthalmitis based on dilated fundoscopy for patients with fungemia at a tertiary care hospital. METHODS: This study was a retrospective chart review of adult patients admitted to the medical centre of the University of Arkansas for Medical Sciences (UAMS) between May 1, 2014 and December 31, 2017, who had positive fungal blood cultures during their hospitalization. RESULTS: There were 324 positive fungal cultures in 290 patients. Of this initial group, there were 161 eye exams. Ocular examination identified 7 of 161 patients (4.3%) with chorioretinitis or endophthalmitis. DISCUSSION: These outcomes along with previous studies support the current guidelines that screening with dilated fundus examination for these patients is appropriate and necessary.

Ocular Outcome of Brazilian Patients With Congenital Toxoplasmosis.

BACKGROUND: Retinochoroiditis is the most frequent manifestation of congenital toxoplasmosis. We aimed to describe the ocular outcome and factors that may influence the visual prognosis of these patients. METHODS: Cohort of patients with confirmed congenital toxoplasmosis seen between 1996 and 2017 in Porto Alegre, southern Brazil. RESULTS: Seventy-seven patients were included, of which 65 (85.5%) were identified by routine screening. Median age at the end of the follow-up was 10 years (minimum 2, maximum 25). Retinochoroiditis was present in 55 patients (71.4%). New retinochoroidal lesions developed after the first year of life in 77.8% of the patients who began treatment after the fourth month of life, compared with 35.2% among those treated before 4 months of life (relative risk = 0.45, 95% confidence intervals: 0.27-0.75, P = 0.02) and 33.3% among those treated before 2 months of life (relative risk = 0.42, 95% confidence intervals: 0.25-0.72, P = 0.01). There was a peak incidence of new retinochoroidal lesions between 4 and 5 years and another peak between 9 and 14 years, the latter only among girls. Thirty-four patients with retinochoroiditis were followed up for 10 years or more, and the school performance was appropriate in 28 (82.4%). CONCLUSIONS: The high incidence of new retinochoroidal lesions during the follow-up period indicates the importance of long-term follow-up of patients with congenital toxoplasmosis. Initiating treatment within the first 4 months of life, especially within the first 2 months, was a protective factor against the later development of retinochoroiditis. Despite the usual favorable prognosis, the high morbidity of congenital toxoplasmosis in Brazil was confirmed.

Clinical and Multimodal Imaging Findings and Risk Factors for Ocular Involvement in a Presumed Waterborne Toxoplasmosis Outbreak, Brazil1.

In 2015, an outbreak of presumed waterborne toxoplasmosis occurred in Gouveia, Brazil. We conducted a 3-year prospective study on a cohort of 52 patients from this outbreak, collected clinical and multimodal imaging findings, and determined risk factors for ocular involvement. At baseline examination, 12 (23%) patients had retinochoroiditis; 4 patients had bilateral and 2 had macular lesions. Multimodal imaging revealed 2 distinct retinochoroiditis patterns: necrotizing focal retinochoroiditis and punctate retinochoroiditis. Older age, worse visual acuity, self-reported recent reduction of visual acuity, and presence of floaters were associated with retinochoroiditis. Among patients, persons >40 years of age had 5 times the risk for ocular involvement. Five patients had recurrences during follow-up, a rate of 22% per person-year. Recurrences were associated with binocular involvement. Two patients had late ocular involvement that occurred >34 months after initial diagnosis. Patients with acquired toxoplasmosis should have long-term ophthalmic follow-up, regardless of initial ocular involvement.

Evolving Longitudinal Retinal Observations in a Cohort of Survivors of Ebola Virus Disease.

Importance: The 2-year ophthalmic sequelae of Ebola virus disease (EVD) in survivors of the 2013 to 2016 epidemic is unknown and may have public health implications for future outbreaks. Objective: To assess the potential for uveitis recurrence, the behavior of dark without pressure, and visual outcomes in a cohort of Sierra Leonean survivors of EVD 2 years following the 2013 to 2016 Ebola epidemic. Design, Setting, and Participants: Prospective, 1-year observational cohort study performed between 2016 and 2017 at 34 Military Hospital, Freetown, Sierra Leone. Participants included survivors of EVD who reported ocular symptoms since Ebola treatment unit discharge and were participants of a previous case-control study. Participants were invited for ophthalmic reexamination and finger-prick blood sampling for immunoglobulin G (IgG) to Toxoplasma gondii and HIV. Exposures: Ebola virus disease. Main Outcomes and Measures: Primary outcome measure: comparative ultra-widefield retinal imaging. Secondary outcome measures: visual acuity and detection of IgG to T gondii and HIV. Results: Of 57 survivors of EVD who underwent repeated ophthalmic evaluation, 37 were women (64.9%). Mean (SD) age was 31.9 (11.1) years. Median interval between first and last examination was 370 days (interquartile range [IQR], 365-397.5 days), and median time from discharge to last examination was 779 days (IQR, 732-821 days). Fifteen eyes of 10 survivors (17.5%) had retinal lesions secondary to EVD. No new EVD-associated retinal lesions were observed. Two survivors (3.5%) developed new posterior uveitis resembling toxoplasmosis chorioretinitis and 41 (73%) were seropositive for T gondii IgG. Areas of dark without pressure were observed either confined to the perimeter of Ebola retinal lesions (n = 7) and non-Ebola lesions (n = 2), involving extensive retinal areas adjacent to Ebola retinal lesions (n = 4) and non-Ebola lesions (n = 2) or in isolation (n = 6). Both expansion and regression of areas of dark without pressure were observed over the study period. Best eye-presenting visual acuity had mild or no visual impairment in 55 survivors (96.4%) 2 years following discharge. Conclusions and Relevance: Vision was maintained in survivors of EVD 2 years following discharge. Evolving regions of dark without pressure may be associated with EVD retinal lesions and might suggest the presence of an ongoing intraretinal stimulus, which may be associated with infective etiology. Treatment strategies should account for the possibility of toxoplasmosis chorioretinitis recurrence within survivors of EVD.

Patterns of Uveitis among Patients Attending Jimma University Department of Ophthalmology, Jimma, Ethiopia.

Introduction: Uveitis is an important cause of blindness and ocular morbidity in the world. The patterns of uveitis have not been well characterized in sub-Saharan Africa. Purpose: To describe the characteristics of uveitis among patients presenting to Jimma University Department of Ophthalmology (JUDO) from July 2013 to December 2014. Methods: This hospital-based prospective cross-sectional study included all new uveitis patients visiting JUDO outpatient department during the study period. Results: Among 98 patients diagnosed with uveitis, anterior uveitis was found in 74.5% of patients. Majority of the patients, 83.7%, had unilateral uveitis. A uveitis syndrome was identified in 22.5% of cases; of these 15 (68.2%) were infectious. Herpes simplex uveitis was the commonest infectious cause (53.3%) while Toxoplasmosis was the most common cause of posterior uveitis (60%). Conclusion: Anterior uveitis was the most common pattern found among uveitis patients. Herpes simplex and toxoplasmic chorioretinitis were the most common-identified infectious causes.

The incidence of endophthalmitis or macular involvement and the necessity of a routine ophthalmic examination in patients with candidemia.

BACKGROUND: The incidence of ocular candidiasis (OC) in patients with candidemia varies across different reports, and the issue of whether routine ophthalmoscopy improves outcomes has been raised. This study investigated the incidence of OC and evaluate whether the extent of OC impacts the clinical outcomes. METHODS: This retrospective study included non-neutropenic patients with candidemia who underwent treatment at one of 15 medical centers between 2010 and 2016. Chorioretinitis without other possible causes for the ocular lesions and endophthalmitis was classified as a probable OC. If signs of chorioretinitis were observed in patients with a systemic disease that causes similar ocular lesions, they were classified as a possible OC. RESULTS: In total, 781 of 1089 patients with candidemia underwent an ophthalmic examination. The prevalence of OC was 19.5%. The time from the collection of a positive blood culture to the initial ophthalmic examination was 5.0 ± 3.9 days in patients with OC. The leading isolate was Candida albicans (77.9%). Possible OC was associated with unsuccessful treatments (resolution of ocular findings) (odds ratio: 0.354, 95% confidence interval: 0.141-0.887), indicating an overdiagnosis in patients with a possible OC. If these patients were excluded, the incidence fell to 12.8%. Endophthalmitis and/or macular involvement, both of which require aggressive therapy, were detected in 43.1% of patients; a significantly higher incidence of visual symptoms was observed in these patients. CONCLUSION: Even when early routine ophthalmic examinations were performed, a high incidence of advanced ocular lesions was observed. These results suggest that routine ophthalmic examinations are still warranted in patients with candidemia.

Assessment of ocular toxoplasmosis patients reported at a tertiary center in the northeast of Iran.

PURPOSE: Ocular toxoplasmosis, which is caused by the single-cell parasite Toxoplasma gondii, is currently the most significant cause of posterior uveitis in the world. No previous studies have described the prevalence and clinical features of ocular toxoplasmosis in the northeast of Iran. The purpose of the current study was to address this gap. METHODS: In this retrospective study, the medical records of 488 uveitis patients who presented to the Khatam-al-Anbia Eye Hospital of Mashhad University of Medical Sciences, a tertiary ophthalmology center in the northeast of Iran, between January 2013 and December 2015 were evaluated. The clinical features and risk factors of 99 (20%) consecutive patients with ocular toxoplasmosis were extracted. RESULTS: Ninety-nine including 53 (53.5%) female and 46 (46.5%) male patients with ocular toxoplasmosis were included in the analysis. Reduced vision (77%) and floaters (15.2%) were the most common presenting symptoms. The age category that was most affected by ocular toxoplasmosis was 20-40 years (range: 11-65 years) with a mean age of 27.2. All patients had retinochoroiditis, but just two had anterior uveitis. All of the extracted patients, with the exception of three patients, had unilateral involvement. None of the patients had any other medical disorders with the exception of one woman, who had diabetes. Only four recurring ocular toxoplasmosis patients were referred to the education hospital during the study. Serology data were available for just 32 patients, of which 31 (96.8%) were IgG positive, and 1 (3.2%) was IgM positive. CONCLUSION: Toxoplasma gondii was responsible for 20% of the patients of uveitis that presented to the largest ophthalmology center in the northeast of Iran. There is a high incidence of patients of ocular toxoplasmosis in the northeast of Iran, and it is a significant cause of uveitis and visual impairment in this area.

Associations between Polymorphisms within Interferon Gamma and Tumor Necrosis Factor Genes and Toxoplasma Retinochoroiditis in Ghanaian Patients.

PURPOSE: To evaluate associations between IFN-γ +874T/A and TNF-α-308G/A polymorphism with the development of Toxoplasma retinochoroiditis. METHODS: By ARMS-PCR, a cross-sectional genetic study involving 30 patients with Toxoplasma retinochoroiditis and 87 controls was carried out. RESULTS: IFN-γ +874: by comparing with the AA genotype, individuals with the TT genotype had a 3.4 odds ratio (OR); AT had a 1.6 OR; and the T allele had a higher OR (1.6), indicating a likely susceptibility of IFN-γ +874T to the infection, though the overall distribution was not significant (p = 0.259). For TNF-α-308G/A, individuals with both GA and AA genotypes had lower ORs when compared with the GG genotype, implying the A allele could confer protection against Toxoplasma ocular lesions. CONCLUSIONS: IFN-γ +874T allele may increase the risk of ocular lesions in Toxoplasma infection. The principle of natural selection seems to also play a role. The less common TNF-308A allelic form could be protective against the development of Toxoplasma ocular infection.

Follow-up of the 1977 Georgia Outbreak of Toxoplasmosis.

In 1977, an outbreak of toxoplasmosis occurred among 37 persons associated with exposure to an indoor horse arena. Cat feces containing the organism were most likely stirred up when horses ran on the dirt floor, and were inhaled or ingested by riders and observers. After 25 or more years, we attempted to locate persons from the outbreak and offer them an eye examination. Of the 37 persons in the outbreak, 18 (49%) were located; four had died, and the remaining 14 agreed to an examination. Among the 14 persons examined, three (21%) were found to have lesions typical of toxoplasmic retinochoroiditis. If these three persons were the only ones with ocular disease among the 37 persons in the outbreak, the disease rate would still be high (8%). As a result of exposure to Toxoplasma gondii during this outbreak, a relatively high percentage of persons developed ocular disease.

PROSPECTIVE TRIAL OF ENDOGENOUS FUNGAL ENDOPHTHALMITIS AND CHORIORETINITIS RATES, CLINICAL COURSE, AND OUTCOMES IN PATIENTS WITH FUNGEMIA.

PURPOSE: Former studies have found rates of endogenous endophthalmitis ranging from 0% to 37% in patients with fungemia. This study sought to prospectively determine the rate and risk factors for endogenous chorioretinitis and endophthalmitis in patients with fungemia. METHODS: A prospective cohort study was performed of consecutive adult inpatients at a single site from 2010 to 2013 of patients with positive blood cultures for fungus. One hundred and nineteen pieces of information were gathered for each patient. RESULTS: A total of 125 patients were enrolled in the study with 7 positive cases of chorioretinitis for a rate of 5.6%. Of these positive cases, 2 patients had endophthalmitis for a rate of 1.6%. Two patients who had a negative initial examination subsequently had a positive examination; 57% of the chorioretinitis patients who could report symptoms were asymptomatic, 57% of the chorioretinitis patients died, and 32% of negative cases died. Prolonged hospitalization, altered mental status, total parenteral nutrition, and gastrointestinal surgery were protective on univariate but not multivariate analysis. CONCLUSION: Despite modern antifungal therapy, fungal chorioretinitis and endophthalmitis continue to occur in patients with positive fungal cultures. Two dilated ophthalmic examinations should still be considered even in asymptomatic patients with fungemia.

Ocular Involvement Following Postnatally Acquired Toxoplasma gondii Infection in Southern Brazil: A 28-Year Experience.

PURPOSE: To determine the incidence of, and risk factors for, ocular involvement among people known to have postnatally acquired Toxoplasma gondii infection in a region of southern Brazil where there is a high prevalence of endemic disease. DESIGN: Retrospective longitudinal cohort study. METHODS: Records of 302 patients with serologic evidence of recent T gondii infection (a positive anti-T gondii IgM antibody test) from Erechim, Rio Grande do Sul state, Brazil (1974-2002) were analyzed. The incidence of ocular involvement was calculated in terms of person-years (PY) of follow-up. Risk factors for ocular involvement were analyzed using log-rank and Fisher exact tests. RESULTS: At initial ocular examination (baseline), 30 patients (9.9%) had intraocular inflammation only (anterior chamber cells and flare, vitreous inflammatory reactions, retinal whitening), without clinically apparent necrotizing retinochoroiditis. At baseline, men were more likely to have ocular involvement (P = .043) and antiparasitic treatment was associated with less ocular involvement (P = .015). Follow-up examinations were performed on 255 patients (median follow-up, 13.7 months [range 0.4-261.9 months]). Among those without ocular involvement at baseline, the incidence of necrotizing retinochoroiditis was 6.4/100 PY. Patients >40 years of age at first IgM test had a greater risk of incident necrotizing retinochoroiditis (hazard ratio = 4.47, 95% CI = 1.67-11.93, P = .003) than younger patients. The incidence of recurrent necrotizing retinochoroiditis was 10.5/100 PY. CONCLUSION: Isolated intraocular inflammatory reactions can be an initial manifestation of T gondii infection, with necrotizing retinochoroiditis occurring months or years later. Male sex and older age are risk factors for toxoplasmic retinochoroiditis. Antitoxoplasmic treatment may protect against early ocular involvement.

Ocular Involvement Following an Epidemic of Toxoplasma gondii Infection in Santa Isabel do Ivaí, Brazil.

PURPOSE: To investigate ocular involvement (prevalence, incidence, lesion characteristics) following postnatally acquired infection with an "atypical" genotype of Toxoplasma gondii during a well-characterized 2001 outbreak in Santa Isabel do Ivaí, Brazil, attributed to a contaminated municipal reservoir. DESIGN: Prospective longitudinal cohort study. METHODS: We performed ophthalmic examinations on 290 of 454 individuals with serologic evidence of T gondii infection during the epidemic (positive IgM antibody tests). Prevalence of ophthalmic findings (intraocular inflammatory reactions [including transient, isolated retinal whitening without clinically apparent retinal necrosis] and necrotizing retinochoroiditis) at initial examination (baseline) and incidence of new findings during 10.5 months of follow-up were calculated. Cumulative risks of ophthalmic events were determined (Kaplan-Meier technique). RESULTS: Ocular involvement was present in 33 of 288 IgM+ individuals (11.5%) at baseline, including 17 with focal retinal whitening only and 13 with necrotizing retinochoroiditis. Incidence of new ocular involvement was estimated to be 1.73 events per 100 person-months (PM); cumulative risk at 10.5 months was 30.1%. Incident necrotizing retinochoroiditis was more common among those with focal retinal whitening at baseline (6.7/100 PM) than among those with no ocular involvement at baseline (1.11/100 PM; hazard ratio 6.07 [1.94-19.01]; P < .0001). CONCLUSIONS: Waterborne infection with an atypical genotype of T gondii is associated with substantial risk of ocular involvement. Lesions may continue to develop during the first year after infection. The increased risk of late necrotizing retinochoroiditis associated with isolated focal retinal whitening at presentation suggests the early presence of parasites in the retina, despite initial lack of observable retinal necrosis.