Understanding Toxoplasmosis in the United States Through "Large Data" Analyses

Abstract

Background: Toxoplasma gondii infection causes substantial morbidity and mortality in the United States, and infects approximately one-third of persons globally. Clinical manifestations vary. Seropositivity is associated with neurologic diseases and malignancies. There are few objective data concerning US incidence and distribution of toxoplasmosis.

Methods: Truven Health MarketScan Database and International Classification of Diseases, Ninth Revision (ICD-9) codes, including treatment specific to toxoplasmosis, identified patients with this disease. Spatiotemporal distribution and patterns of disease manifestation were analyzed. Comorbidities between patients and matched controls were compared.

Results: Between 2003 and 2012, 9260 patients had ICD-9 codes for toxoplasmosis. This database of patients with ICD-9 codes includes 15% of those in the United States, excluding patients with no or public insurance. Thus, assuming that demographics do not change incidence, the calculated total is 61 700 or 6856 patients per year. Disease was more prevalent in the South. Mean age at diagnosis was 37.5 ± 15.5 years; 2.4% were children aged 0-2 years, likely congenitally infected. Forty-one percent were male, and 73% of women were of reproductive age. Of identified patients, 38% had eye disease and 12% presented with other serious manifestations, including central nervous system and visceral organ damage. Toxoplasmosis was statistically associated with substantial comorbidities, including human immunodeficiency virus, autoimmune diseases, and neurologic diseases.

Conclusions: Toxoplasmosis causes morbidity and mortality in the United States. Our analysis of private insurance records missed certain at-risk populations and revealed fewer cases of retinal disease than previously estimated, suggesting undercoding, underreporting, undertreating, or differing demographics of those with eye disease. Mandatory reporting of infection to health departments and gestational screening could improve care and facilitate detection of epidemics and, thereby, public health interventions.

Keywords: ICD-9 code; Toxoplasma gondii; Truven Health MarketScan Database; toxoplasmosis; “large data”.

Figure 1.

Demographic statistics of cohort, 2003–2012. A, Age at first diagnosis with toxoplasmosis. Increasing numbers of patients were diagnosed with toxoplasmosis as a function of age, indicating that there is an increasing disease burden among older individuals, who are potentially more capable of moving through the environment and engaging in risky behaviors, including the consumption of undercooked food, which pose the threat of exposure to infectious oocysts and ingestion of contaminated materials. More females than males were identified with toxoplasmosis in this cohort (approximately 59% vs 41% of the total number of cases). The ratio of male to female was most similar early on in the patient's lifetime, whereas there was an increasing disparity skewing toward increased incidence in females. This could be explained by screening of women of reproductive age, or could potentially indicate a difference in risk of exposure to the pathogen. B, Map of toxoplasmosis prevalence by county in the United States. Darker regions indicate increased prevalence of the infection. States with highest prevalence include Texas, California, New York, Illinois, Georgia, Florida, Maryland, and South Carolina. All these states had >400 patients with toxoplasmosis over the study period. There are pockets of increased prevalence across the southern United States. This is consistent with previous studies indicating increased prevalence among rural populations, with increased risk of environmental exposure.

Figure 2.

Clinical manifestations of toxoplasmosis, 2003–2012. Expected annual incidence of toxoplasmosis by disease manifestation in the United States. Using the number of identified cases of toxoplasmosis over the 10-year study period, recognizing that a previous estimate indicated the database accounted for 15% of the total population of the United States, and dividing this by the total number of years of the study, an estimated annual incidence of toxoplasmosis was found as a function of disease manifestation. These values represent the first quantitation of some of these manifestations for the United States in more than a decade.

Figure 3.

Venn diagram showing numbers of patients who were diagnosed by International Classification of Diseases, Ninth Revision (ICD-9) codes for toxoplasmosis with and without codes for medicines. Abbreviation: TMP-SMX, trimethoprim-sulfamethoxazole.