Half the victims of the legionnaires' disease outbreak visited Christchurch Hospital this year, but health authorities have ruled it out as a source.
An elderly woman from northern Christchurch is the 19th patient in the outbreak that has health officials stumped. Three people have died.
Canterbury Medical Officer of HealthDr Mel Brieseman said about half of the victims had been to the hospital as patients, outpatients or visitors this year. Two were inpatients during the disease's incubation period.
But Dr Brieseman said the hospital visitor trends further ruled it out as a source of the infection. Most of those diagnosed were elderly with pre-existing health problems.
"The latest case only adds to the fact that it is not a simple picture," Dr Brieseman said.
Routine in-house testing found the legionella bug in Christchurch Hospital's hot-water system last year. The system was shock-treated with bleach to kill the bug.
Dr Brieseman was aware the bug had been found in the past and was confident that the hospital's testing regime was "comprehensive".
The hospital had been monitoring its building using the Canterbury District Health Board's laboratory. The building had now been checked by staff, independent auditors and Environment Canterbury.
