Pig-linked disease outbreak in China ebbs

Aug 17, 2005 (CIDRAP News) – The outbreak of an unusual pig-related disease in China might be nearly spent, and evidence continued to point to Streptococcus suis as the cause, the World Health Organization (WHO) said yesterday.

Chinese authorities reported 215 cases, including 39 deaths, nearly all of them in farmers and butchers who had been killing sick pigs or processing and selling the meat, the WHO said. The outbreak has been concentrated in Sichuan province.

As of yesterday, no new cases had been reported since Aug 5, the agency said. Today, however, Agence France-Presse (AFP) reported a new case in a 44-year-old butcher who works in the fresh pork section of a Hong Kong supermarket. He was reported to be hospitalized in stable condition.

"The data provided by the Chinese depict an outbreak that peaked from the second through the fourth week of July, and dwindled rapidly thereafter," the WHO statement said.

Lab tests on samples from several patients identified S suis serotype 2, and the same strain was found in pigs in the area, the agency reported. Tests on the human samples detected no other bacterial agents. Authorities considered the possibility of a viral infection in the pigs, but tests excluded influenza and Nipah virus infections.

The WHO said a group of international experts on S suis discussed the outbreak in an Aug 9 teleconference. "Overall, the specialists expressed no concern related to the validity of the laboratory identification of Streptococcus suis serotype 2," the agency said. "The clinical picture, they felt, could be explained by a strain or strains of Streptococcus suis with a higher virulence in humans."

Early in the outbreak, patients were suspected of having a hemorrhagic fever with renal syndrome, but lab tests excluded that, the WHO said. The signs and symptoms included high fever, malaise, nausea, and vomiting. In severe cases, patients suffered meningitis, subcutaneous hemorrhage, toxic shock, and coma.

Infectious disease expert Michael T. Osterholm, PhD, MPH, said the illness resembles some other forms of streptococcal and staphylococcal disease involving toxic shock. "Based on the information that the Chinese have provided, I think the explanation seems quite reasonable that this was a strain of S suis that may have acquired the potential to produce a yet-unidentified toxin or toxins," he told CIDRAP News.

"If you look at staphylococcal and streptococcal toxic shock syndromes, every one of those was an instance where certain toxin-producing capabilities in the staph and strep organisms changed," Osterholm added. He is director of the University of Minnesota Center for Infectious Disease Research and Policy, publisher of this Web site.

Chinese authorities found no evidence of person-to-person transmission of the disease, including transmission to healthcare workers, the WHO said. Specialists involved in the teleconference said person-to-person spread was unlikely without close contact with infective material such as blood. They also said that eating raw or undercooked pork could lead to disease, but eating properly cooked pork is unlikely to pose a risk.

According to the WHO, Chinese officials said more study is needed to find out why the outbreak was so large, relative to previous outbreaks of the fairly rare disease, which was first recognized in humans in the 1960s.

The international specialists and Chinese authorities agreed that the movement of live pigs and trade in pork within and from the outbreak area should be carefully regulated, the WHO said.

The butcher who fell ill in Hong Kong had not traveled outside the city but had cut his finger, the AFP story said. The meat at the Wellcome Supermarket where he worked had not come from Sichuan, and officials were investigating how the man contracted the disease, a Wellcome spokeswoman told a local radio station.