METHODS: A case-case analysis compared culture-positive and culture-independent Campylobactercases reported to Pennsylvania’s electronic disease surveillance system during 2009-2014 using unadjusted and age- and sex-adjusted logistic regression.
RESULTS: In Pennsylvania during 2009-2014, 6,831 culture-positive and 2,586 culture-independent cases were identified. When compared to culture-positive cases, culture-independent cases were more likely to be female (OR=1.2, 95% CI: 1.1-1.4) and >65 years old (OR=2.0, 95% CI: 1.8-2.2). The seasonal distribution of reported onset dates differed, with culture-independent cases being less likely to report onset during May-October (aOR=0.7, 95% CI: 0.6-0.8). Culture-independent cases were less likely to report diarrhea (aOR= 0.5, 95% CI: 0.4-0.7), abdominal pain (aOR=0.8, 95% CI: 0.7-0.9), and fever (aOR=0.5, 95% CI: 0.4-0.6), but were more likely to report vomiting (aOR = 1.3, 95% CI: 1.2-1.4). Culture-independent cases were more likely to have severe outcomes of hospitalization (aOR=1.6, 95% CI: 1.4-1.8) and death (aOR=4.4, 95% CI: 1.9-10.3). Culture-independent cases were less likely to report several exposures, including history of animal contact (aOR=0.8, 95% CI: 0.7-0.9), eating ≥1 meal(s) outside the home (aOR=0.7, 95% CI: 0.7-0.8), consuming undercooked meat (aOR=0.8, 95% CI: 0.6-0.9), swimming (aOR=0.7, 95% CI: 0.6-0.9), international travel (aOR=0.4, 95% CI: 0.4-0.6), and consumption of unpasteurized dairy products or juices (aOR=0.6, 95% CI: 0.4-0.7). There were no differences identified for consumption of well water or undercooked eggs. Additionally, there were no differences identified with respect to laboratory type (hospital or commercial).
CONCLUSIONS: This comparison identified multiple significant differences in demographic, clinical, and epidemiologic factors between culture-positive and culture-independent Campylobacter cases reported during 2009-2014 in Pennsylvania. These findings are consistent with previous comparisons, and identify additional significant differences in reported epidemiologic risk factors. These results raise questions about the true case-positivity rate among culture-independent cases. Clinical laboratories should confirm positive culture-independent results using Campylobacter stool culture. In 2015, the CDC case definition changed to classify positive culture-independent test results as probable rather than suspect campylobacteriosis cases. These findings suggest further analyses may be warranted to evaluate the impact of this case definition change.