01 August, Manila - On 22 July 2005, an outbreak of an unknown illness involving 20 cases and nine deaths in Sichuan Province, China, was reported to WHO by the Chinese Ministry of Health.
By 1 August, an intensive investigation conducted by provincial and national teams (including retrospective case finding) had revealed a total of 181 possible cases associated with 34 deaths. China has been diligent in supplying information on the situation through daily updates of new case numbers. In addition, extensive information from the field investigation has been posted on the website of China’s Center for Disease Control.
A parallel investigation by animal health authorities into illness and deaths in pigs occurring in the same part of Sichuan Province has revealed evidence of infection by a bacterium called Streptococcus suis. This bacterium is commonly found in pigs all over the world and is usually asymptomatic, although it can cause illness and sometimes death.
Early findings from the human outbreak investigation showed a high proportion of cases involved slaughtering pigs, preparing them for consumption or eating them. Subsequent investigations have shown evidence of Streptococcus suis infection in 19 of the suspected cases. None of the human cases appears to have had contact with any other cases.
On the basis that the outbreak is caused by Streptococcus suis, the Government response team has applied extensive control measures, including steps to identify infected pigs, to protect people from the risk of infection through public health education, as well as to the identify and treat human cases.
Sporadic cases of human Streptococcus suis infection are known to occur worldwide, usually through occupational contact with pigs. Many cases are not serious, but in a significant minority, severe manifestations, including meningitis and toxic shock syndrome (TSS) can occur and may result in death. However, outbreaks of Streptococcus suis infection are unusual. In addition, although many of the clinical features described in the outbreak are consistent with Streptococcus suis infection, the apparent proportion of patients showing severe illness and the level of mortality appear relatively high. However, this may reflect the easier identification of more serious cases at the beginning of the investigation
Any outbreak that shows unusual or previously unreported features requires a thorough clinical, laboratory investigation to obtain a complete picture. Collaboration between animal and human health authorities to determine the factors underlying the extent of the outbreak and in coordinating the detection of cases and public health responses will be vital.