The low-tech solution could help prevent the spread of airborne infections such as tuberculosis -- and ironically, old-fashioned hospitals with high ceilings and big windows may offer the best design for this, they reported.

They worked better than modern "negative pressure" rooms, with expensive design aimed at pumping out infected air, the researchers report in the Public Library of Science journal PLoS Medicine.

"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," wrote Rod Escombe of Imperial College London and colleagues in their report.

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

For their report, Escombe and colleagues tested the air in eight hospitals in Lima, Peru.

Wards built more than 50 years ago, with large windows and high ceilings, had better ventilation than modern rooms that relied on natural ventilation.

And they were also superior to the mechanically ventilated rooms, they reported in their study, available online at http://medicine.plosjournals.org/perlserv/?request=get-document& doi=10.1371/journal.pmed.0040068.

Tuberculosis is spread by bacteria that can float in the air and the researchers calculated what their findings might mean for the spread of TB.

They estimated that in mechanically ventilated rooms, 39 percent of susceptible people would become infected after 24 hours of exposure to an untreated TB patient. This compared to a 33 percent infection rate in modern rooms with windows open and 11 percent in a pre-1950-style room.

"We found that opening windows and doors provided median ventilation of 28 air changes/hour, more than double that of mechanically ventilated negative-pressure rooms ventilated at the 12 air changes an hour recommended for high-risk areas," they wrote.

Experts are looking at these factors in trying to prepare for a pandemic of influenza.

"The current practice of sealing in the local environment is probably the wrong route for hospital wards," Peter Wilson of University College London Hospitals added in a commentary on the study.