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All cases of hepatitis A were laboratory confirmed according to the Diagnostic Criteria of Viral Hepatitis A (WS 298-2008) (1). Based on date of onset, 3,511 HA cases were reported nationwide through NNDRS between January 1, 2020 and March 18, 2020, which was a decrease of 12.3% compared with the 4,003 cases reported across the nation during the same period last year. In contrast, HA cases reported from Liaoning Province in January 1 through March 18 increased from 700 in 2019 to 1,361 in 2020, accounting for approximately one-third of all cases reported nationwide. After integration of the HA vaccine into the national Expanded Program on Immunization (EPI) in 2008, HA had occurred at relatively low levels in Liaoning with periodic increases in every 3–5 years, and the most recent increase was in 2014–2016. In 2020, the number of reported HA cases increased markedly in the first 2 months of the year but began to decrease on March 4 (Figures 1 and 2).
Figure 1.Weekly reported hepatitis A (HA) cases in Liaoning Province, 2004 through Week 11 of 2020.
Figure 2.Seafood sales timeline and daily distribution of reported hepatitis A (HA) cases in Liaoning, October 1, 2019 to March 18, 2020.
There were 426 and 586 cases reported from two coastal cities, Dalian and Dandong, which accounted for 74.36% (1,012/1,361) of all cases reported from Liaoning. Zhuanghe County of Dalian and Donggang County of Dandong reported 262 (62.50%, 262/426) and 290 (49.49%, 290/586) cases, which was more than any other county (Figure 3).
Figure 3.Geographic distribution of Hepetitis A (HA) reports in Liaoning Province and two local areas, January 1, 2020 to March 18, 2020. (A) County level distribution of reported HA cases in Liaoning Province. (B) Township-level distribution in Zhuanghe County, Dalian City. (C) Township-level distribution in Donggang County, Dandong City.
Most cases were among adults that were aged 30–54 years in Dalian and aged 30–49 years in Dandong, which represented 85.4% (364/426) and 82.6% (484/586) of the cases in the two cities. There were 4 (0.39%, 4/1,012) reported cases among children less than 15 years of age, and 3 of the 4 children had no history of HAV vaccination. By occupation, 50.9% (515/1,012) of HA cases were among farmers and 31.2% (316/1,012) were among household workers or unemployed individuals.
Local CDCs conducted routine epidemiological investigations of all reported and confirmed HA cases in face-to-face or telephone interviews (n=191). The interviews focused on five themes including eating habits, drinking water, types of seafood eaten, dining-out behavior, and sources of food during their incubation period. We analyzed data from case interviews conducted between January and early March in Zhuanghe County and found that 71.2% (104/146), 36.9% (31/84), and 13.3% (2/15) of interview subjects who consumed oysters, snapping shrimp, or cockles ate them raw. During the same time in Dandong, the percent of HA cases with a history of seafood consumption in 2020 was 84.7% (287/339), which was higher than in 2018 (72.0%) and 2019 (61.0%) (local, unpublished data).
We compared sales of local seafood during the two months prior to the HA increase with sales during the HA epidemic. We found that HA case reports began to increase in December 2019, approximately one month after local seafood became available in November. Following a sharp increase of seafood sales during Spring Festival in January 2020, there was a peak of HA cases in February and early March (Figure 2).
The case-control study was conducted by Dalian CDC using face-to-face and telephone interviews. All 191 confirmed HA cases reported between January 1, 2020 and March 7, 2020 in Zhuanghe County were enrolled as the case group, and 277 healthy individuals residing in the same county were recruited for the control group. Controls were healthy adults living in the same town as a case, with no history of HA, and who had not received HAV vaccine. The questionnaire was designed, tested, and revised by Dalian CDC; all data, including eating habits, types of drinking water, types of seafood eaten, food sources, and dining out behavior, were collected by trained, experienced local staff. HA risk factors were identified by univariate and multivariate logistic regression analyses. We found that consumption of raw or undercooked seafood (OR=11.1, 95% CI: 6.0–20.6), eating clams (OR=2.5, 95% CI: 1.6–5.9), eating snapping shrimp (OR=3.1, 95% CI: 1.6–6.0), and eating oysters (OR=4.6, 95% CI: 2.6–8.1) were significantly associated with HAV infection (Table 1).
Item Cases (N=191) Controls (N=277) Univariate analysis Multivariate analysis Number Percentage (%) Number Percentage (%) OR (95% CI) OR (95% CI) Consumption habits Eating raw seafood 64 33.5 41 14.8 12.0 (6.6–21.9) 11.1 (6.0–20.6) Dining out 60 31.4 35 12.6 3.1 (1.9–5.1) 1.4 (0.7–2.7) Types of seafood eaten Big yellow corbicula 43 22.5 23 8.3 3.5 (2.0–6.2) 1.1 (0.4–2.8) Little yellow corbicula 31 16.2 20 7.2 2.4 (1.3–4.5) 0.3 (0.1–0.8) White corbicula 71 37.2 62 22.4 2.0 (1.3–3.1) 1.0 (0.5–1.8) Mixed color corbicula 22 11.5 11 4.0 3.5 (1.6–7.9) 2.5 (0.8–7.4) Sand corbicula 72 37.7 64 23.1 2.1 (1.4–3.3) 0.9 (0.5–1.7) Clams 41 21.5 17 6.1 4.7 (2.4–9.0) 2.5 (1.6–5.9) Snapping shrimp 84 44.0 46 16.6 4.4 (2.6–7.2) 3.1 (1.6–6.0) Cockle 15 7.9 9 3.2 2.5 (1.4–6.1) 1.8 (0.5–6.2) Oysters 146 76.4 97 35.0 6.1 (3.8–10.0) 4.6 (2.6–8.1) Table 1. Case-control study on risk factors of Hepetitis A (HA) in Dalian City, Liaoning Province, 2020.
In March 2020, we collected 30 samples of seafood from local markets, 23 samples of seafood from coastal areas, and 3 samples of water from the Yellow Sea estuary. The samples were sent to the National Marine Environment Monitoring Center to test for the presence of HAV. All samples were negative for HAV.
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