Case-case analyses of cryptosporidiosis and giardiasis using routine national surveillance data in the United States - 2005-2015.

K M Benedict,E P Marder,M C Hlavsa,S A Collier,K E Fullerton,J S Yoder

doi:10.1017/s0950268819000645

Abstract

Understanding endemic infectious disease risk factors through traditional epidemiological tools is challenging. Population-based case-control studies are costly and time-consuming. A case-case analyses using surveillance data addresses these limitations by using resources more efficiently. We conducted a case-case analyses using routine surveillance data reported by 16 U.S. states (2005-2015), wherein reported cases of salmonellosis were used as a comparison group to identify exposure associations with reported cases of cryptosporidiosis and giardiasis. Odds ratios adjusted for age and reporting state (aOR) and 95% confidence intervals (95% CI) were calculated. A total of 10 704 cryptosporidiosis cases, 17 544 giardiasis cases, and 106 351 salmonellosis cases were included in this analyses. When compared with cases of salmonellosis, exposure to treated recreational water (aOR 4.7, 95% CI 4.3-5.0) and livestock (aOR: 3.2; 95% CI: 2.9-3.5) were significantly associated with cryptosporidiosis and exposure to untreated drinking (aOR 4.1, 95% CI 3.6-4.7) and recreational water (aOR 4.1, 95% CI 3.7-4.5) were associated with giardiasis. Our analyses shows that routine surveillance data with standardised exposure information can be used to identify associations of interest for cryptosporidiosis and giardiasis.

Highlights

Cryptosporidiosis and giardiasis are nationally notifiable gastrointestinal illnesses caused by the parasites Cryptosporidium and Giardia, respectively
Case–control studies are a common and preferable way to identify risk factors. Because both cryptosporidiosis and giardiasis, such as other enteric illnesses, are underreported to public health agencies, the source population from which the reported cases arise almost certainly differs from the characteristics of randomly-selected, illness-free general population controls which are required to produce an unbiased causal effect in case–control studies
To avoid biases introduced by these differences, researchers have suggested selecting cases of another disease from among those captured by the same surveillance system to serve as the control or comparison group to estimate differential risk [5]

Summary

Introduction

Cryptosporidiosis and giardiasis are nationally notifiable gastrointestinal illnesses caused by the parasites Cryptosporidium and Giardia, respectively. We used the case–case analyses approach with national surveillance data to identify associations of interest for sporadic cryptosporidiosis and giardiasis in the United States. States routinely transmit reports of cases and related epidemiological, laboratory and limited exposure data to NNDSS using integrated surveillance information systems in public health departments.

Results

Conclusion