Public Health Surveillance and Reporting for Human Toxoplasmosis

Six States, 2021

Jayden McCall; Laura Rothfeldt, DVM; Kelly Giesbrecht, DVM; Amanda Hunt; Leah Bauck, MPH; Joni Scheftel, DVM; Rachael Birn, MPH; Bryan Buss, DVM; Betsy Schroeder, DVM; Thomas E. Haupt, MS; Rachel Klos, DVM; Anne Straily, DVM


Morbidity and Mortality Weekly Report. 2022;71(28):889-893. 

In This Article

Abstract and Introduction


Toxoplasmosis is caused by infection with the zoonotic parasite Toxoplasma gondii. Although disease tends to be mild (e.g., self-limiting influenza-like symptoms) or asymptomatic in immunocompetent persons, toxoplasmosis is more severe in immunocompromised persons, who can develop potentially fatal encephalopathy.[1] In addition, primary infections acquired during pregnancy might result in a range of adverse outcomes, including fetal ocular infection, cranial and neurologic deformities, stillbirth, and miscarriage.[1,2] An estimated 11% of the U.S. population aged ≥6 years are seropositive for toxoplasmosis, based on analysis of sera collected through the National Health and Nutrition Examination Survey during 2011–2014.[3] Toxoplasmosis is not a nationally notifiable disease in the United States, and currently no national public health surveillance data are available; however, it is reportable in eight states. To better understand how surveillance data are collected and used, reviews of state-level toxoplasmosis surveillance were conducted during June–July 2021 using semistructured interviews with health officials in six states (Arkansas, Kentucky, Minnesota, Nebraska, Pennsylvania, and Wisconsin) where toxoplasmosis is currently reportable. Why or when toxoplasmosis became reportable could not be determined, and many of the states had limited capacity to respond to reported cases. Case definitions varied considerably in terms of clinical description, laboratory criteria, and case classification (i.e., confirmed, probable, or suspect), limiting disease estimates and comparisons among states. Implementation of a standardized case definition would help ensure that cases are counted consistently, enabling better use of surveillance data to characterize disease. Identifying newly acquired cases is challenging because most acute cases among immunocompetent persons (including pregnant women) are asymptomatic, disease among immunocompromised persons is likely reactivation of latent disease, and congenital infections might not manifest until later in life.

Members of the family Felidae (cats) are definitive hosts for T. gondii. Humans can be infected through various routes, including fecal-oral contamination from cats; consumption of undercooked contaminated meat, contaminated unwashed fruits or vegetables, contaminated water, and unpasteurized milk; vertical transmission from an infected mother; and organ transplantation. Toxoplasmosis is likely underdiagnosed in the United States: approximately 90% of infections among immunocompetent persons are asymptomatic or nonspecific and self-limiting;[1] when symptoms are present, they can potentially mimic other more frequently encountered illnesses, including influenza and tickborne-diseases such as Lyme disease or anaplasmosis; thus, physician awareness and clinical suspicion of toxoplasmosis might be low, resulting in delays in or missed opportunities for diagnosis and case identification.[4,5] No national maternal toxoplasmosis screening program currently exists, and most infants born with congenital toxoplasmosis appear normal at birth.[1,2] Because reactivation of toxoplasmosis during immunocompromise can be rapidly fatal, and outcomes of congenital infection can be severe, toxoplasmosis surveillance could help improve awareness and understanding of disease prevalence and transmission routes and identify opportunities for prevention and control.

States where toxoplasmosis is reportable were identified using the State Reportable Conditions Assessment query tool on the Council of State and Territorial Epidemiologists (CSTE) website* and supplemented by reviewing reportable diseases lists accessed from state health department websites for inclusion of toxoplasmosis. A modified version of a qualitative questionnaire used for Chagas disease surveillance[6] was developed to identify why toxoplasmosis was designated a reportable condition in the state, how cases are reported and by whom, what actions are taken after case identification, how surveillance data are used and disseminated, whether nonhuman data are collected and used, and whether formal toxoplasmosis maternal screening programs are in place.[6] State public health veterinarians were contacted by email and invited to participate either by telephone or virtual interview or to complete the questionnaire. The purpose and scope of the project, as well as a copy of the questionnaire, were included in this initial email. This activity was reviewed by CDC and was conducted consistent with applicable federal law and policy.

As of April 2021, toxoplasmosis is reportable in eight states (Arkansas, Delaware, Hawaii, Kentucky, Minnesota, Nebraska, Pennsylvania, and Wisconsin); among these states, public health personnel from six (Arkansas, Kentucky, Minnesota, Nebraska, Pennsylvania, and Wisconsin) agreed to participate and were interviewed. The historic dates when toxoplasmosis became reportable and the reasons for initiating surveillance could not be determined. Toxoplasmosis had been reportable for as long as could be remembered and reviewing historical case data could not further elucidate a starting date. Several possible reasons were suggested for why toxoplasmosis was made reportable, including monitoring disease prevalence, a need to identify the source of infection, the effect of toxoplasmosis on pregnancy, congenital transmission, and outbreak identification. In addition, whether any substantial changes had occurred in how surveillance data were collected since toxoplasmosis became reportable also could not be determined.

Case definitions were provided by the states and varied considerably in both clinical and laboratory criteria and how cases are classified (Table). Variations in clinical descriptions included a separate description for immunocompromised persons (all states except Arkansas and Minnesota); a separate description for infection acquired during pregnancy (Kentucky, Nebraska, and Wisconsin); further separation based on timing of infection during pregnancy (early versus late; Pennsylvania); and a category for chronic infection status (Minnesota). Signs and symptoms used in each clinical description category were similar but not consistent. Variations in laboratory criteria included whether paired or sequential antibody testing was confirmatory (all states except Arkansas and Pennsylvania); single antibody titers as presumptive/suggestive criteria (Arkansas and Kentucky); criteria for congenital infection in infants (Kentucky, Nebraska, and Wisconsin); and a criterion that included testing at a reference laboratory (Minnesota). Among the variations in case classification were that Nebraska and Wisconsin had only a "confirmed" case classification and no "probable" classification, Pennsylvania also included a "suspect" classification, and Minnesota's case classifications specified "confirmed," "probable," and "chronic."

After notification of a case, all states attempt to investigate to determine exposure and clinical history; however, investigation depends on resource availability. Laboratories are the primary reporting source in all states, although physicians might also report cases. No state reported having formal maternal screening programs for toxoplasmosis; however, maternal screening is frequently recorded as the reason for testing on case report forms submitted to the state health department (Minnesota). No states collected nonhuman data as a routine part of toxoplasmosis surveillance. The Nebraska state public health veterinarian indicated that their office receives data from the state veterinary diagnostic laboratory about toxoplasmosis diagnosed in animals. Although such reports contain the animal owner's city and zip code, they do not name the owner and are not formally integrated with the human case surveillance program.

Dissemination of surveillance data occurs through public reports posted to state health department websites (Arkansas, Minnesota, and Wisconsin) or updates to toxoplasmosis case counts in annual disease tables available on the state health department website (Kentucky). In two states (Nebraska and Pennsylvania), reports are distributed internally within the agency, but not externally.

45 C.F.R. part 46; 21 C.F.R. part 56.