Table 1.
Epidemiological features of four groundwater-borne norovirus-associated outbreaks in Gyeonggi province, South Korea between 2008 and 2012
| Outbreak no. | 2008-A* | 2011-B† | 2012-C | 2012-D |
|---|---|---|---|---|
| Epidemiological study | Retrospective cohort | Case-control | Retrospective cohort | Retrospective cohort |
| Outbreak setting | Water park | Five schools | Restaurant | Restaurant |
| Duration of exposure | 14 Jan. 2008 | 16–19 May 2011 | 23–25 May 2012 | 30 May 2012 to 1 June 2012 |
| Date of onset | 16 Jan. 2008 | 18–20 May 2011 | 25 May 2012 | 1 June 2012 |
| Median incubation time | 36 h | 24 h | 26 h | 41 h |
| Median age (range) | 12 yr (11–30 yr) | 16 yr (8–19 yr) | 19 yr (18–45 yr) | 16 yr (15–41 yr) |
| Outbreak-associated illnesses (no. ill/no. exposed) | 31·0% (67/216) | 5·9% (451/7605) | 75·9% (22/29) | 74·5% (76/102) |
| Suspected exposure route | Unknown | Cabbage kimchi | Unknown | Unknown |
| Relative risk or odds ratio | n.d. | 1·65–4·55 | n.d. | n.d. |
| Clinical specimens | ||||
| Total (n). | 3 | 149 | 22 | 39 |
| Norovirus positive (n) | 3 | 51 | 7 | 15 |
| Genotype (n) | GI.4 (3) | GI.3 (51) | GII.17 (7) | GII.2 (15) |
| Groundwater | ||||
| Date of collection | 21 Jan. 2008 | 20 May 2011 | 29 May 2012 | 4 June 2012 |
| Collection points (n) | Water park reservoir | Food plant groundwater (2) | Camp groundwater | Restaurant tap |
| Filtered volume (litres) | 670 | 436–640 | 505 | 531 |
| Norovirus genotype (n) | GI.4 | GI.3 (2) | GII.17 | GII.2 |
| Homology‡ | >98·9% | >99·4% | >96·6% | 100·0% |
| Disinfection system | Sand filtration, Chlorination | Ultraviolet light | None | Chlorination |
| Total coliforms | Positive | Positive | Positive | n.d. |
| E. coli. | Positive | Positive | Positive | n.d. |
| Distance to septic tank | n.d. | 10 m | 20 m | n.d. |