Table 2. Studies comparing the prevalence of foodborne trematode infections in villages close to water bodies with distant villages*.
| Study site, period (reference) | Population sample | Characteristics of water body | Prevalence | RR (95% CI) |
|---|---|---|---|---|
| Asillo irrigation area, Peru, 1999 (26) | 338 school children | 500-hectare irrigation area with irrigation canals and drainage channels | Fasciola hepatica: 18.8%, 20.3%, 31.3% in 3 schools in irrigation scheme | NA |
| Kimhae county, Republic of Korea, 1974 (27) | 1,809 | River region | Clonorchis sinensis: 72.1% near riverside and 41.3% inland | 1.74 (1.57–1.92) |
| Goyang county, Republic of Korea, 1974 (27) | 578 | River region | C. sinensis: 32.7% near riverside and 6.3% inland | 5.16 (3.04–8.75) |
| Hadong Gun, Republic of Korea, 1978 (28) | 1,163 | Rivers and streams | Metagonimus yokogawai: 5.4%–90.8% in villages close to river and streams and 4% in village 4 km from river | 7.44 (2.83–19.54) |
| Pohang industrial belt, Republic of Korea, 1989 (29) | 3,180 employees; 200 for questionnaire analysis | Hyungsai River basin | C. sinensis: 52% of infected employees lived near river compared with 27.9% of uninfected employees | 1.85 (1.28–2.67) |
| Okcheon-gun, Republic of Korea, 2000 (30) | 1,081 | Geum-Gang River | C. sinensis: 14.2% of inhabitants near river were infected with C. sinensis compared with 3.2% of inland residents | 4.51 (2.64–7.70) |
| Metagonimus spp.: 8.4% of inhabitants near river were infected, compared with 1.7% of inland residents | 5.01 (2.40–10.46) | |||
| Nong Wai irrigation area, Khon Kaen, Thailand, 1974–1975 (31) | 627 children | Irrigation canal and channels | Opisthorchia viverrini: 7.3% in irrigated villages and 3.3% in nonirrigated villages | 2.20 (0.87–5.51) |
| Nam Pong development project, Khon Kaen province, Thailand, 1977–1978 (21) | 3,183 | Reservoir and irrigation scheme | O. viverrini: 27.1% in irrigated villages and 17.2% in traditional villages (no irrigation) | 1.63 (1.34–2.00) |
| O. viverrini: 10.8% lakeside and 11.5% in resettlement areas | 0.93 (0.66–1.31) | |||
| Chonnabot village, Khon Kaen province, Thailand, 1980–1982 (32) | 4,638; 246 included for incidence calculation | Wide shallow reservoirs that remained dry in 1981–1982 | O. viverrini: 47% in uninfected individuals becoming positive within 1 year while reservoirs were flooded and 20% during period when reservoirs were dry† | 2.17 (1.42–3.29) |
| 18 villages in Nong Khai and Loei provinces, Thailand, 1981–1982 (33) | 1,259 | Khong River and Huang River (flowing water) | O. viverrini: 51.7% and 52.6% in villages >5 km from river and 27.9% and 21.7% in villages closer to river | 0.47 (0.40–0.56) |
| 12 provinces of Vietnam, 1994–2000 (34) | >20,000 | Red River delta region | C. sinensis: £31% in coastal delta region, 5% in mountainous area, and 16.3% in highlands. O. viverrini: highest in urban coastal areas | NA |
| Mantaro valley, Peru, 2000 (35) | 206 children | Small streams | Odds ratio 17.22 | |
| All studies | 2.15 (1.38–3.36) |
*RR, relative risk; CI confidence interval; NA, not available. †Incidence values.