Preventing the spread of infections like tuberculosis may be as simple as opening a window, researchers say.

"Opening windows and doors maximizes natural ventilation so that the risk of airborne contagion is much lower than with costly, maintenance-requiring mechanical ventilation systems," the researchers wrote in Tuesday's online issue of the Public Library of Science journal PLoS Medicine.

"Old-fashioned clinical areas with high ceilings and large windows provide greatest protection. Natural ventilation costs little and is maintenance free," they added.

Officials with the World Health Organization have recommended natural ventilation to limit the transmission of TB in poor areas, but until now there has been no evidence that it works.

Tuberculosis bacteria spread by floating in the air, and cases occur mainly in tropical areas, so Rod Escombe of Imperial College London and his colleagues compared the ventilation provided by the low-tech solution to modern fans in hospitals.

The researchers compared eight hospital wards in Lima, Peru, including 70 rooms built before 1950 with natural ventilation and 12 modern rooms with mechanical ventilation.

Breath of fresh air

Even at the lowest wind speeds, natural ventilation beat mechanical ventilation, the team found.

Applying a mathematical model of airborne infection, the researchers estimated what percentage of people would be susceptible to infection after being exposed to untreated TB patients for 24 hours.

The findings were:

• 39 per cent for patients in a mechanically ventilated room.
• 33 per cent in a modern, naturally ventilated rooms.
• 11 per cent in a pre-1950 room naturally ventilated with open windows and doors.

Well-maintained negative-pressure isolation rooms are ideal for high-risk areas of hospitals, but they neglect other important areas of potential transmission such as crowded emergency departments and waiting rooms, the study's authors said.

In a commentary accompanying the study, Peter Wilson of University College London suggested looking at natural ventilation in flu pandemic preparations.

Although "natural ventilation is not an easy solution for patients in countries where winters are cold … the current practice of sealing in the local environment is probably the wrong route for hospital wards," Wilson concluded.

During Toronto's outbreaks of SARS in 2003, health officials in Ontario said all hospitals should preferably isolate patients in a negative pressure room, or if that is not possible, then in a single room with the door closed.