UV light 'could curb TB spread'

TB is caused by infection with mycobacterium tuberculosis

Installing ultraviolet lights could reduce the spread of tuberculosis (TB) in hospital wards and waiting rooms by 70%, research suggests.

The move could potentially save many lives globally, particularly where hospital patients are crowded together.

TB infects more than nine million, and kills nearly two million people a year world-wide, and drug resistant strains are becoming more widespread.

The international study features in the journal PLoS Medicine.

Plans are already underway to install ultraviolet lights in the chest clinic at St Mary's Hospital, London - the first hospital to have them in the UK.

When people are crowded together in a hospital waiting room, it may take just one cough to infect several vulnerable patients Dr Rod Escombe Imperial College London

When a TB patient coughs, bacteria are sprayed into the air in tiny droplets, floating around the room and infecting other patients, visitors and healthcare staff.

But the latest study has shown that these bacteria can be killed by hanging a shielded short-wave ultraviolet-C (UVC) light from the ceiling with a fan to mix the air.

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.

Researcher Dr Rod Escombe, from 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."

Dr Escombe said TB infection rates in the UK were low, and patients could usually be treated with antibiotics.

But the disease took a much more deadly toll in developing countries, where drug resistant strains were more of a menace, and there were limited resources for isolating patients.

Introducing UVC lights could be a relatively low-cost measure, say the researchers. Currently, a typical UVC ceiling light costs around US$350 and replacement bulbs cost from US$25.

Guinea pig tests

In the current study, UVC lights were hung in a hospital ward in Lima, Peru, where 69 patients with TB and HIV 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.

Some animals received air exposed to the UV lights on the ward, some air treated with negative ionisers, and some untreated air straight from the ward.

By the end of the experiment, 35% of the animals exposed to untreated air were infected with TB, with 8.6% going on to develop the active form of the disease.

In comparison, just 9.5% of the animals exposed to the UV-treated air became infected with TB, and just 3.6% went on to develop active disease.

Dr Cath Noakes, from the University of Leeds, who also worked on the study, said the impact of UV lights was maximised by careful management of air flow on the wards.

She said: "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."