Disease Risks at Sichuan (WHO) part 1

Risk factors for increased communicable disease burden

1. Interruption of access to safe water and sanitation facilities. The populations displaced by the
earthquake are at immediate and high risk of outbreaks of water/sanitation/hygiene-related and foodborne diseases such as cholera, shigellosis due to Sd1, typhoid fever, and hepatitis A and E.

2. Population displacement with overcrowding. Populations in the affected areas and relief centres are at immediate risk of diseases spread by respiratory transmission such as measles and pneumonia. Increased risk of meningitis is also associated with overcrowding.

3. Increased exposure to disease vectors. Displacement of populations due to earthquake-related destruction of housing can result in increased exposure to disease-carrying vectors, including those for Japanese encephalitis.

4. Poor access to health services is of immediate concern. The degradation of the health infrastructure and of the means of communication prevent access to usual services, as well as to emergency medical and surgical services put in place in response to this crisis.

5. When deaths result from a natural disaster, exposure to dead bodies is not associated with
disease transmission. There is no evidence that corpses pose a risk of epidemics after natural
disasters. Standard infection control precautions should be observed when handling human corpses.


PRIORITY COMMUNICABLE DISEASES

Water/sanitation/hygiene-related and foodborne diseases

The displaced populations in China are at high risk from outbreaks of water, sanitation, and hygienerelated diseases, as well as foodborne diseases, due to reduced access to safe water and sanitation systems.

Disruption of usual water sources and contamination of water by destroyed sewage infrastructure may result in unsafe drinking-water being consumed, increasing the risk of exposure. Cholera has been reported in Sichuan Province recently, and the strengthening of prevention and treatment of cholera has been a focus of the MoH. Salmonella typhi (causing typhoid fever), hepatitis A and hepatitis E, and Shigella dysenteriae type 1 (Sd1) are also present and have epidemic potential. Diarrhoea is a major cause of under five mortality; WHO estimates that diarrhoea accounts for 12% of under-five deaths in China.

Leptospirosis is a bacterial zoonosis present worldwide. Infection in humans may occur indirectly when the bacteria comes into contact with the skin (especially if damaged) or the mucous membranes. It can also result from contact with moist soil or vegetation contaminated with the urine of infected animals, or with contaminated water as a result of swimming or wading in floodwaters, accidental immersion or occupational abrasion.

Vector-borne diseases

Population displacement can result in an increased exposure to vectors, and therefore to vector-borne diseases. Additionally, movement of susceptible populations into higher-risk areas can increase the risk of transmission. With the vast destruction associated with this earthquake, pools of water suitable for vector breeding may develop with subsequent rains.

Japanese encephalitis (JE) occurs in the Asian region, transmitted by the Culex mosquitoes which breed particularly in flooded areas and rice fields. Inadequate shelter, rains in the earthquake-affected area, and the disruption of vector control programmes due to the earthquake could lead to an increased exposure to vectors.

The virus circulates in Ardeidae birds (herons, egrets), and pigs act as amplifying hosts for the
virus. (Sichuan Province is a major pig-producing source for China and neighbouring countries).

Humans are incidental hosts, and infection occurs primarily in children. A national programme to vaccinate schoolage children against JE free of charge has recently commenced, but coverage is estimated to be low.

Culicine mosquitoes are normally zoophilic (feeding mainly on animals) but may also bite humans. China CDC maintains an annual surveillance and monitoring of JE in this region. Vector control methods and personal protection information can be found in section 3.7.

Human plague cases have been reported in the past in the mountain regions of Sichuan, where known natural foci for Yersinia pestis circulate among the wild rodents and their fleas. The disturbance of the natural enzootic cycle can result in increased contact between the wild and domestic rodent populations increasing the chance of exposure of people to potentially infective rodents. Populations displaced by the earthquake may be at higher risk of exposure to rats and fleas carrying Y. pestis, not only in Sichuan but possibly in surrounding provinces where plague is endemic (including Gangsu, Xinghai, Yunnan, and Guizhou). Detection and management of cases, as well as methods for control of pests and environmental contamination, should follow MoH guidance.

There is no significant risk of malaria transmission within the earthquake-affected areas of Sichuan Province. Although malaria remains a serious public health problem in China, it occurs primarily in Yunnan and Hainan Provinces where risk of transmission of P. falciparum is high. The Province of Sichuan reported 289 cases in 2003 (accounting for <1% of total malaria cases reported by the country.

Aedes aegypti,, the primary vector for dengue is currently not reported in Sichuan Province. Aedes albopictus, a secondary vector for dengue, is present in Sichuan Province. China reported less than 600 cases of dengue in 2007, primarily in provinces further south.