Almost 100 sick in Chinese Clostridium perfringens outbreak

Almost 100 people fell sick in a Clostridium perfringens outbreak in China in 2024.

In May 2024, an elderly care center in Beijing reported dozens of acute diarrhea cases. The local Center for Disease Control and Prevention opened an epidemiological investigation to identify the outbreak’s source and implement control measures.

According to a report in the journal China CDC Weekly, the first case was a 49-year-old female staff member who developed diarrhea. The patient’s symptoms resolved without medical intervention or medication.

An investigation identified 77 elderly residents and 21 staff cases, ranging in age from 22 to 99. This included 38 males and 60 females. All patients had diarrhea but no severe cases were recorded.

At the time of the investigation, the facility had 485 elderly residents and employed 204 staff. A centralized kitchen and dining facility served meals to both residents and staff.

A case-control study included 24 confirmed/probable cases and 70 controls. Face-to-face dietary history investigations focused on breakfast and lunch consumption on one day in May. This revealed 88 percent of cases had consumed Chinese hamburgers compared with 51 percent of controls.

Chinese hamburgers were identified as the suspected food vehicle. A total of 23 patient samples and one burger sample tested positive for Clostridium perfringens.

Risk from slow cooling process
Chinese Hamburger (Roujiamo), is a traditional dish consisting of a bun stuffed with chopped braised pork. The braising process, known as “lu” in Chinese cuisine, involves simmering over low heat followed by a cooling period to enhance flavor.

The preparation process for the pork filling in Chinese hamburgers included portioning, blanching and simmering in broth, followed by natural cooling.

According to kitchen staff, raw pork was refrigerated upon purchase. Pork might have been contaminated during production, transportation or storage. The following day, the pork was portioned, blanched for 20 minutes, and simmered in spiced broth for 40 minutes.

Researchers said because of the high thermal resistance of Clostridium perfringens, combined with the possibility that large batches of meat may not have been thoroughly heated, the bacteria could form spores during this process, enabling survival.

After cooking, the pork was left to cool naturally while submerged in the broth. This slow cooling process potentially allowed Clostridium perfringens to proliferate and produce toxins. Cooled pork was later chopped and combined with cilantro and green peppers before being stuffed into buns.

Researchers said rapid cooling through the critical temperature range of 15 to 55 degrees C (59 to 131 degrees F) may effectively prevent bacterial proliferation. They also recommended comprehensive training for food handlers on proper cooling procedures when preparing Chinese hamburgers.

Investigators collected 86 samples including 50 patient samples, 13 anal swabs from healthy kitchen staff, 11 food samples, and 12 environmental swabs. Overall, 23 patient samples and one food sample tested positive by PCR.

Public health interventions included reassignment of kitchen staff with a recent history of diarrhea to non-food handling positions.

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