LONDON -- Britain's worst outbreak of legionnaires' disease in a decade claimed its sixth victim late Friday, a woman aged in her 50s, AFP quoted as health officials saying.

They said the woman died in the intensive care unit of the royal Lancaster infirmary, north west England, where several of the 140 infected patients have been treated.

An 88-year-old man along with a 76-year-old woman and three other women in their fifties have also died since the outbreak began in the northwest region of Cumbria at the start of August.

The disease was traced to a 30-year-old air conditioning system at an arts center.

Legionnaires' disease -- first discovered at an American legion convention in July 1976 where 29 people died -- causes high fever, dry cough, lung congestion and subsequent pneumonia.

It is commonly spread through contaminated air conditioners and ventilators, and is treated with antibiotics.