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Table 3 Comparison on positive rates of environmental surveillance for H7N9 virus, by three waves — Zhejiang Province, China, March 2013-February 2015

From: Human infection and environmental contamination with Avian Influenza A (H7N9) Virus in Zhejiang Province, China: risk trend across the three waves of infection

Characteristics 1st wave 2nd wave 3rd wave Total Trend χ2 value P value
Towns, % (positive towns/total towns) 5.6 (5/90) 19.5 (69/354) 37.1 (104/280) 32.0 (161/503) 45.996 <0.001
Premises, % (positive premises/total premises) 2.8 (5/181) 11.0 (98/890) 28.2 (138/490) 16.0 (238/1488) 91.319 <0.001
Environmental samples of different premises, % (positive specimens/total specimens) 0.7 (11/1499) 4.3 (376/8647) 11.8 (481/4061) 6.1 (868/14207) 335.989 <0.001
 Live poultry markets 1.4 (7/511) 6.5 (374/5786) 15.1 (404/2669) 8.8 (785/8966) 203.645 <0.001
 Poultry rearing farms 0.7 (4/541) 0.2 (2/1263) 0.0 (0/489) 0.3 (6/2293) 5.558 0.029
 Concentrated areas of backyard poultry farms 0.0 (0/247) 0.0 (0/1074) 0.8 (2/250) 0.1 (2/1571) 6.302 0.049
 Slaughtering and processing plants 0.0 (0/17) 0.0 (0/141) 9.1 (17/186) 4.9 (17/344) 13.232 <0.001
 Habitats for migratory birds 0.0 (0/86) 0.0 (0/134) 0.0 (0/103) 0.0 (0/323) - -
 Others 0.0 (0/97) 0.0 (0/249) 15.9 (58/364) 8.2 (58/710) 48.346 <0.001
Environment samples of different types, % (positive specimens/total specimens) 0.7 (11/1499) 4.3 (376/8647) 11.8 (481/4061) 6.1 (868/14207) 335.989 <0.001
 Fecal dropping swab 0.3 (2/702) 2.8 (94/3306) 9.7 (174/1786) 4.7 (270/5794) 145.342 <0.001
 Poultry cage swabs 0.0 (0/315) 5.4 (106/1956) 11.3 (85/750) 6.3 (191/3021) 55.669 <0.001
 Drinking water samples 1.0 (2/201) 2.9 (27/943) 10.1 (34/338) 4.3 (63/1482) 31.962 <0.001
 Sewage from cleaning poultry 1.5 (1/67) 5.0 (43/859) 20.2 (61/302) 8.6 (105/1228) 62.802 <0.001
 Swabs of tables for slaughtering or processing poultry 1.6 (1/61) 7.3 (78/1063) 14.6 (93/636) 9.8 (172/1760) 28.542 <0.001
 Others 3.3 (5/153) 5.4 (28/520) 13.7 (34/249) 7.3 (67/922) 18.342 <0.001