Update on Outbreak Associated With Streptococcus Suis in Pigs in China

BEIJING -- As China moves towards concluding its investigation into the recent outbreak in Sichuan Province associated with Streptococcus suis in pigs, the Ministry of Health of China has shared more details with WHO about the outbreak.  A group of international specialists on Streptococcus suis convened by WHO has assessed, based on the information provided by the Ministry of Health, that the outbreak in humans is compatible with Streptococcus suis etiology.

To date, the Ministry of Health of China has reported 215 cases of human

disease associated with the outbreak.  Of these human cases, 39 have been

fatal.  No new cases have been reported since Aug. 5.  The data provided by

China depict an outbreak that peaked from the second through the fourth week

of July, and dwindled rapidly thereafter.  Authorities say several human cases

were discovered retrospectively, once the epidemiological investigation was

underway.

The initial cases were suspected of having haemorrhagic fever with renal

syndrome, but laboratory tests ruled that out.  More cases were reported, with

a range of clinical presentations -- high fever, malaise, nausea and vomiting,

followed by meningitis, subcutaneous haemorrhage, toxic shock and coma in

severe cases.  Nearly all of the patients were reported to be local farmers

and butchers by profession, about 80 percent of them men, who had been killing

sick pigs or processing and selling the meat.  More than 40 percent of the

cases were aged between 50 to 60 years.

Subsequently, laboratory tests on several of the human samples confirmed

infection with Streptococcus suis serotype 2.  A concurrent investigation by

the Ministry of Agriculture of China discovered the presence of Streptococcus

suis serotype 2 in pigs in the area.  Authorities say tests on human samples

have not shown the presence of any other bacterial agent.  A viral etiology

was also considered in pigs, and both influenza and Nipah virus infections

were reported to have been ruled out.

Authorities add that based on their investigation so far there is no

evidence of human-to-human transmission, and no healthcare workers tending to

the patients have been infected.  The Ministry of Health says further study is

still needed, however, to try to determine why this outbreak was so large,

including so many fatalities, especially compared to previous outbreaks in

recent years.

A group of international specialists on Streptococcus suis, including WHO

technical staff, held a teleconference on Aug. 9 to discuss this outbreak.

Overall, the specialists expressed no concern related to the validity of the

laboratory identification of Streptococcus suis serotype 2.  The clinical

picture, they felt, could be explained by a strain or strains of Streptococcus

suis with a higher virulence in humans.

The specialists reiterated that Streptococcus suis is a relatively rare

disease in humans.  It was first identified in humans in the 1960s, and few

outbreaks in humans have been reported around the world since then.  Even

though the Streptococcus suis genome has been sequenced globally, the

specialists noted, the function of 20 percent to 30 percent of the genome is

still unclear.

The specialists suggested that further testing on samples from the Sichuan

outbreak might be helpful, as would comparisons between the strain associated

with this outbreak and strains linked to other occurrences in the past in

China and other countries.  Chinese authorities have indicated that they are

keen for such studies to be conducted.

The specialists also noted the lack of epidemiology to suggest person-to-

person spread in the present outbreak -- including the absence of cases among

children -- and considered this reassuring.  They said person-to-person

transmission was unlikely to occur unless there was very close contact with

infected material such as blood (something that would almost only occur in

hospital settings).

The group reiterated that although consumption of raw or undercooked pork

may lead to disease, eating properly cooked pork is unlikely to represent an

increased risk, even if the strain of Streptococcus suis involved is more

virulent.  This outbreak once again raises the wider global issue of the links

between -- on the one hand -- food safety, animal husbandry and slaughtering

practices (especially in poor, backyard farms and rural areas), and, on the

other hand, an ever-growing range of zoonotic diseases.

Regarding a possible national and international spread of the outbreak,

the specialists concurred with the Chinese authorities that the movements of

live pigs, and the trade of pig carcasses and meat within and from the

outbreak area, had to be carefully regulated and monitored.  China says it has

put strict measures in place to ensure this.

Source: World Health Organization