Evaluation of Cryptosporidiosis Surveillance in Ohio, 2006-2013

BACKGROUND:   Cryptosporidiosis was added to the Nationally Notifiable Conditions list in 1995 and has undergone four case classification revisions (1998, 2009, 2011, and 2012) because of evolving laboratory methods. These revisions have had a major impact on capacity of state and local public health agencies to meet reporting requirements. Ohio added Cryptosporidiosis to the Ohio Reportable Infectious Diseases List in April of 1995. We evaluated the Ohio Disease Reporting System (ODRS) to assess the effect of revisions on case reporting and secondarily assess for completeness and timeliness. We developed recommendations to overcome identified limitations.

METHODS:   We surveyed Ohio laboratories on current Cryptosporidium laboratory methods being used. We analyzed Ohio’s surveillance data from 2006 and 2013 and calculated case-classification changes and quantified the number of confirmed cases potentially being reported as probable due to limitations in laboratory testing methods. Additionally, we assessed for completeness (proportion of interviews completed) and timeliness (lag time between event date and report date). 

RESULTS:   Sixty percent (50/84) of laboratories responded to the survey. Respondents reported 64 percent of Ohio’s Cryptosporidiosis cases reported between 2006 and 2013. Eighty-four percent of respondent laboratories used a single testing method for Cryptosporidium. Of these, 38 percent employed the Immunochromatographic card/rapid card test. Between 2011 and 2013, 306 cases of Cryptosporidiosis were classified as probable, a lower level of certainty than the gold standard. Surveillance data indicated the proportion of probable cases increased from 5 percent in 2010 to 71 percent in 2011. Between 2006 and 2013 no trend was observed in either completeness or timeliness. The proportion of interviews completed ranged from 68 percent to 85 percent (median, 79). Moreover, the average lag time for Cryptosporidiosis case reporting ranged from eight to eleven days (median, 9).

CONCLUSIONS:   Numerous changes to the Cryptosporidiosis case definition have had a substantial impact on capacity to meet current confirmed case classifications. Rapid clinical diagnostic methods, while appropriate for patient care, complicate surveillance. We recommend (1) Ohio laboratories consider implementing laboratory testing methods sufficient to classify Cryptosporidiosis cases as confirmed; (2) the Council of State and Territorial Epidemiologists (CSTE) align new clinical testing methods with the legacy test as an equivalent classification; and (3) CSTE limit the frequency of revisions made to the Cryptosporidiosis case definition to allow state and local public health agencies adequate time to adapt to revisions.