Table 2. Contamination factors of foodborne norovirus outbreaks reported to the National Outbreak Reporting System and CaliciNet, United States, August 2009–July 2015.
| GII.4 outbreaks | non-GII.4 outbreaks | P-value‡ | |
|---|---|---|---|
| n = 258 | n = 235 | ||
| Outbreak contributing factor known, n (%)1 | 129 (50%) | 111 (47%) | |
| Contaminated raw product, n (%) | 10 (8%) | 8 (7%) | 1.0 |
| Cross-contamination, n (%) | 6 (5%) | 6 (5%) | 1.0 |
| Food worker implicated, n (%)2 | 94 (73%) | 88 (79%) | 0.3 |
| Bare hand contact, n (%) | 54 (57%) | 45 (51%) | 0.5 |
| Gloved hand contact, n (%) | 23 (24%) | 29 (33%) | 0.3 |
| Other hand contact, n (%) | 30 (32%) | 24 (27%) | 0.5 |
| Level of preparation, n (%)3 | 82 (81%) | 58 (81%) | |
| Eaten raw, n (%) | 61 (60%) | 47 (65%) | 0.5 |
| Heat processed, n (%) | 32 (32%) | 15 (21%) | 0.1 |
| Point of contamination, n (%)4 | 135 (49%) | 140 (51%) | |
| Before preparation, n (%) | 3 (2%) | 8 (6%) | 0.2 |
| Preparation, n (%) | 132 (98%) | 132 (94%) | 0.2 |
1At least one contributing factor (not C-N/A, P-N/A, or S-N/A listed) is selected. Multiple contributing factors may be selected for each outbreak; therefore, the sum of contributing factors may be larger than the number of outbreaks with a known contributing factor.
2Among the outbreaks with at least one known contributing factor (not C-N/A, P-N/A, or S-N/A listed) is selected (n = 244).
3Among the outbreaks with at least one implicated food item listed (n = 173). Multiple levels of preparation may be selected for each outbreak; therefore, the sum of level of preparation methods may be larger than the number of outbreaks with a known level of preparation
4Among the outbreaks where point of contamination listed as either before preparation or preparation (n = 275).
‡Statistical comparisons made between GII.4 and non-GII.4 outbreaks. Chi-square test was used to compare the outbreak contributing factors, level of preparation, and point of contamination.