A surveillance program for E. coli O157 created after a major outbreak in a Chinese city has recorded a decline in the pathogen.

A large and long outbreak of diarrhea, which included cases of hemolytic uremic syndrome (HUS) caused by E. coli O157:H7, occurred in Xuzhou City and nearby areas from 1999 to 2000 in China. The main source was water and food contaminated with human and animal feces. Around 20,300 infections, 195 HUS patients, and 177 deaths were recorded.

Measures to control the spread of disease included investigation of diarrhea patients, identification of the pathogen, and looking at epidemiological characteristics. Following the outbreak, Xuzhou launched a health campaign focusing on managing water, diet, feces, and eliminating flies. 

A surveillance program was rolled out in 2001 in Tongshan District, Xuzhou City based on the national O157 system and the event in Jiangsu Province. It included 18 towns for patients with diarrhea and food surveillance and three farming towns for animal surveillance.

Surveillance results from 2001 to 2021 showed there was a significant decrease in the isolation rate of O157, found the study published in China CDC Weekly.

E. coli O157 declined after the outbreak
Between 2001 and 2021, raw and cooked meat samples, as well as fecal samples from patients with diarrhea, cattle, sheep, chickens, and pigs were collected. Isolated strains were analyzed for the detection of certain virulence genes. During the outbreak from 1999 to 2000, samples mostly came from affected villages and towns. 

Analysis of O157:H7 isolation rates between host animals, diarrhea patients, and meat samples from 2001 to 2021 was performed. The 20-year surveillance period revealed that rates from animal feces, meats, and patients were 31 out of 7,539, three from 2,526, and four from 5,491.

During the earlier O157:H7 outbreak, isolation rates were 154 out of 1,136 in the feces of host animals, seven of 161 in meat, and 52 from 1,339 in the feces of diarrhea patients.

Between 1999 and 2000, isolation rates of O157:H7 were eight of 41 from cattle, 57 out of 299 from sheep, 34 out of 310 from chickens, and 39 out of 297 from pigs.

Surveillance from 2009 to 2021 showed the isolation rates of feces from cattle, sheep, and pigs were down to 11 out of 1,049 for cattle, six of 1,100 for sheep, and two of 963 for pigs. Also, O157 was not found in chicken feces.

Scientists isolated 22 strains of O157:H7 between 2009 and 2021. Findings indicated that non-Shiga toxin-producing EHEC O157:H7 strains have become dominant.

“Compared to the outbreak period, the isolation rates of O157:H7 from various types of samples were significantly reduced after surveillance sites were established in 2001,” said researchers.

“However, the pathogen was still prevalent in the feces of animal hosts, with cattle and sheep being the main carriers. Therefore, it is necessary to enhance health education among farmers, especially among individual free-range households, to regulate the proper disposal of host animal fecal waste. This action is essential to prevent the spread and infection of O157:H7.”

In Xuzhou, sporadic human infections with O157 have been reported, but there have been no clusters in recent years. This may be due to improved health education and hygiene practices, as well as a decrease in the rate of O157 infection among diarrheal patients said scientists.

“As China’s national economic level improves, people’s living habits are changing, and there is an increase in the number of people who eat green organic vegetables, especially raw food. Therefore, we need to pay attention to the change in this transmission pattern,” they added.