London School of Hygiene & Tropical Medicine

The simple act of washing your hands with soap, which reduces the risk of diarrhoea by half in both developed and developing countries, could also be the key to preventing the spread of acute respiratory infections such as SARS. So say Dr Valerie Curtis and Professor Sandy Cairncross of the London School of Hygiene & Tropical Medicine in a systematic review published this month in the Lancet Infectious Diseases.

Diarrhoea kills 2 million young children every year, with acute respiratory infections claiming the lives of 3.5 million, mainly in the developing countries, even before SARS burst upon the world. A recent study by the US Navy found that hand washing could also reduce the risk of these respiratory infections by 45% (Ryan et al. 2001).

'It is surprising that most of the e-mails and articles written so far about the SARS epidemic make no mention of hand washing as a simple preventive measure', they comment. 'It has been mentioned that the area of Southern China where SARS originated is well known for its intensive duck- and pig-rearing, which is believed to have helped other viruses to cross the species boundary in the past. The agriculture of rural China is also well known for its intensive use of human excreta. Those applying the excreta to the field often become contaminated, and many of them do not wash their hands thoroughly afterwards. China's unhygienic agriculture may have played a part in the transmission of the early SARS cases'.

'It came as a surprise to many that investigators looking into the SARS outbreak in Hong Kong were examining the sewage system of a block of flats in Amoy Gardens', comment the authors. 'This is because many people see the prevention of faecally transmitted diseases such as diarrhoea as completely distinct from the control of infections transmitted in airborne droplets, when "coughs and sneezes spread diseases"'.

But in fact, say the authors, there are two possible links. The first is that the pathogens which cause diarrhoea can also cause respiratory symptoms. This is true particularly of the enteric viruses, such as those which cause "gastric 'flu". Unlike most enteric bacteria, enteric viruses are invasive and if they cause irritation to the epithelial cells in the gut they are also likely to irritate the epithelial cells in the lungs. It follows that the viruses emitted when we cough may also be found in our faeces. Indeed, in some species such as ducks (intensively cultivated in the area of China where SARS originated), influenza is known to be transmitted by the faecal route rather than by aerosol (Shortridge 1997).

The second connection is that both respiratory and enteric pathogens are often transmitted on surfaces, and that the surface we most often use to inoculate ourselves with infection is the skin of our hands. For example, in one study (Corley et al. 1987) children aged 4 to 8 were trained not to touch their nose and eyes so frequently, and this led to a 47% reduction in laboratory-diagnosed common cold infections. We know that viruses such as the cold virus can remain viable on surfaces for several hours (Sattar et al. 1993), that the number needed to cause infection can be very small, and that people can pick up virus particles on their hands by touching objects and surfaces contaminated by aerosols from infected people (Ansari 1991).

'Evidence from the SARS outbreaks tends to confirm the view that a more intimate contact is needed for transmission than simply being present in the same room, train or aeroplane as a SARS victim. Many of the cases have been among those caring for SARS patients', the authors conclude.

The authors are working with soap companies and the World Bank to establish a global partnership to promote handwashing worldwide (www.globalhandwashing.org) and also planning a randomised controlled trial of hand washing as a measure to control both diarrhoea and acute respiratory infections.

Ends.

To contact either of the authors please contact the School's Press Office on 020 7927 2073.

References
Ansari SA et al. Journal of Clinical Microbiology 1991; 29: 2115-2119.
Corley DL, et al. Journal of Pediatric Psychology 1987; 12: 519-531.
Curtis V, Cairncross S, Lancet Infectious Diseases 2003; 3: 275-281.
Ryan MAK, Christian R, Wohlrabe J. Am J Prev Med 2001; 21 (2): 79-83
Sattar SA et al. Applied & Environmental Microbiology 1993; 59: 1579-1585.
Shortridge KF. Journal of Medical Microbiology 1997; 46: 813-815.