Ultraviolet lights could reduce the spread of tuberculosis in hospital wards and waiting rooms by 70 per cent, says a new study, Upper-Room Ultraviolet Light and Negative Air Ionization to Prevent Tuberculosis Transmission published in PLoS Medicine today.

The study, which explored the transmission of tuberculosis (TB) from infected patients to guinea pigs, suggests that installing simple ultraviolet C (UVC) lights in hospitals could help reduce the transmission of TB, including drug-resistant strains.

UVC light is very damaging to tuberculosis bacteria, including multi- and extensively drug-resistant strains, but is safe to humans in the low intensities that reach the lower part of the room where occupants are. Overexposure causes a sunburn-like effect on the skin and can irritate the eyes, but reactions only last 24 hours.

Every year, over nine million people are infected with tuberculosis and nearly two million people die from the disease, according to the World Health Organisation. Infection rates are particularly high in places where vulnerable people are crowded together, such as hospitals, homeless shelters and prisons.

There are two types of TB infection - latent and active. Patients with active TB experience the symptoms of the disease, which include fever, persistent cough, and loss of appetite, and these patients can transmit the disease by coughing. In contrast patients with the dormant, 'latent' form of TB do not have symptoms, and are not infectious.

About 10 per cent of latent TB patients develop active TB over their lifetimes (although this figure rises to over 40 per cent if they have HIV infection as well). Treatment can prevent many patients with latent TB from progressing to active TB. About 95 per cent of TB patients with drug-sensitive disease can be cured with antibiotics, but this figure is much lower in patients with drug-resistant TB disease.

When a tuberculosis patient coughs, bacteria are sprayed into the air in tiny droplets, floating around the room and infecting other patients, visitors and healthcare staff. These bacteria can be killed by hanging a shielded UVC light from the ceiling with a fan to mix the air, say the researchers, from Imperial College London, the University of Leeds, Hospital Nacional Dos de Mayo, Lima, Perú and other international institutions.

In this study, researchers hung UVC lights from the ceiling, with a shield to protect people from direct exposure. In this way the upper part of the room was flooded with high intensity UVC light, but the lower part of the room was safe. During the study, patients, doctors and nurses wore UV exposure monitors and nobody reported overexposure.

UVC light kills tuberculosis bacteria, including drug-resistant strains, by damaging their DNA so they cannot infect people, grow or divide. It is already used at high intensity to disinfect empty ambulances and operating theatres.

Dr Rod Escombe, the study's principal investigator from the Wellcome Trust Centre for Clinical Tropical Medicine at Imperial College London, said, "When people are crowded together in a hospital waiting room, it may take just one cough to infect several vulnerable patients. Our previous research showed that opening windows in a room is a simple way to reduce the risk of tuberculosis transmission, but this is climate-dependent - you can't open the windows in the intensive care ward of a Siberian hospital for example."

"Thankfully, the rate of tuberculosis infection in countries like the UK is relatively low and people who are infected can be treated using antibiotics, which are readily available here. People are more likely to die from the disease in developing countries like Perú, because there are limited resources for isolating patients, diagnosing them quickly and starting effective treatment. Also, the prevalence of drug-resistant TB is much higher in the developing world. Preventing infection is much easier and cheaper than treating a patient with tuberculosis," added Dr Escombe.

Previous research has shown that in a dry atmosphere, a higher proportion of bacteria are killed by UVC light. Perú is very humid and UVC is still effective, therefore it could be even more effective at preventing TB infections in drier countries, or in the air-conditioned environments of health care facilities in the developed world.

Plans are already underway to install upper room UV lights in the chest clinic at St Mary's Hospital, London, which will be the first hospital to have them in the UK.

Introducing UVC lights could be a relatively low-cost measure, say the researchers. Currently, a typical UVC ceiling light costs around $350 and replacement bulbs cost from $25. The researchers are now working to develop more affordable $100 units.

The impact of UV lights is greatest when combined with careful management of the air flow on the wards, as Dr Cath Noakes from the University of Leeds' Faculty of Engineering explains, "The lights must be set high enough to ensure patients and health workers are not overexposed, but if the lights only treat air at that level, there will be little benefit. To be most effective, ventilation systems need to create a constant flow of treated air down to patient level, and potentially infected air up towards the lights."

To reach their conclusions, scientists hung UVC lights in a hospital ward in Lima, Perú where 69 patients with HIV and TB were being treated. The researchers pumped air from the ward up to a guinea pig enclosure on the roof of the hospital for 535 consecutive days. The guinea pigs were split into three groups of approximately 150 - the first group received air exposed to the UV lights in the ward, the second group received ward air treated with negative ionisers, and the third control group was given untreated air straight from the ward. The guinea pigs were given skin tests for tuberculosis once a month.

By the end of the experiment, 35 per cent of the control group were infected with TB, compared to 14 per cent of the ionised air group and 9.5 per cent of the UVC group. 8.6 per cent of the control group developed the active form of the disease after being infected with TB, compared to 4.3 per cent of the ionised air group and 3.6 per cent of the UVC group.

This research was funded by the Wellcome Trust, Sir Halley Stewart Trust and the Sir Samuel Scott of Yews Trust, Proyecto Vigia (USAID) and the charity Innovation for Health and Development (IFHAD).

The freely available research paper is available on http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.1000043