Impact of the New National Surveillance Case Definition on Babesiosis Reporting — Connecticut, 2001–2013

BACKGROUND:   Babesiosis is a potentially life-threatening tickborne and transfusion-associated parasitic disease. Connecticut Department of Public Health (CDPH) has conducted babesiosis surveillance since 1989. In 2011, CDPH adopted the Council for State and Territorial Epidemiologists’ new national surveillance case definition that includes laboratory and clinical criteria. Previously, cases were defined solely by laboratory testing. Since 2011, CDPH contacts health care providers to obtain clinical information for each report meeting laboratory criteria; reports from nonresponding providers are excluded from case counts. We evaluated the impact of the new case definition on babesiosis reporting.

METHODS:  We compared reports received by CDPH during 2001–2010 and 2011–August 31, 2013. We assessed demographics, predictive value positive (PVP), and staff time to process reports. We used chi-square to compare proportions and Wilcoxon rank sum to compare continuous variables. 

RESULTS:   During 2001–2010, 1,786 reports met laboratory criteria; PVP was 97.3%.  During 2011–2013, 1,280 reports met laboratory criteria, of which 772 were excluded because of provider nonresponse; PVP was 21.5%. Median patient age increased from 58.0 (range: 0–98) to 61.0 (range: 0–100) years (P < 0.001); proportion of males increased from 54.7% to 66.3% (P <0.01). Median staff time increased from 12.7 (range: 6.6–28.0) to 200.0 (range: 184.5–255.5) hours/year (P <0.01). Median annual cases decreased from 152 (range: 79–334) to 82 (range: 69–124) (P >0.05); continuing the previous case definition would have resulted in 170 cases/year (range: 146–335) during 2011–2013.

CONCLUSIONS:   Adoption of the new national surveillance case definition corresponded to changes to the reported epidemiology of babesiosis and increased the surveillance burden. The change limits understanding of babesiosis trends in Connecticut.