A cluster of six cases of bovine tuberculosis in Britain suggests the cow illness may spread by human-to-human contact, say researchers who traced transmission of the disease between patrons of a bar and a nightclub.

Human infections with Mycobacterium bovis were relatively common in the late 19th and early 20th centuries, but dairy pasteurization laws and the culling of infected cows has reduced cases.

In this week's issue of the medical journal the Lancet, Jason Evans of the Health Protection Agency and his colleagues described 20 cases of humans infected with bovine tuberculosis in 2005, including six that seem to have resulted from person-to-person transmission.

Of the six cases, five had pulmonary disease, and one patient died from M. bovis meningitis.

Agricultural links were initially suspected for the first three cases but did not pan out, and cases four through six did not live in a rural area, the researchers said. 

Public health investigators turned to molecular techniques and found the cluster of six had a strain that was genetically indistinguishable.

Nightclub scene

A questionnaire revealed the first three people attended the same bar, and they had opportunities to infect the last three at a nightclub in Birmingham, study co-author Grace Smith said in an interview podcasted by the journal.

Because of the pulmonary disease, the patients would have been coughing up infectious aerosols for months. The loud atmosphere of a nightclub, where people tend to shout, is conducive to spreading infections, said Smith, who also works at the agency.

"This report of several instances of M. bovis transmission between people in a modern urban setting emphasizes the need to maintain control measures for human and bovine tuberculosis," Smith said, noting person-to-person transmission remains rare.

Standard public health measures applied to regular human tuberculosis, such as identifying and treating cases, should also be applied to stop airborne person-to-person spread of bovine TB, agreed Charles Thoen, a professor of veterinary microbiology at Iowa State University in Ames and Dr. Philip LoBue from the Centers for Disease Control and Prevention in Atlanta.

Investigations are needed to learn more about the relative importance of bovine tuberculosis in humans, especially in developing countries and countries with widespread HIV infection, since that increases the risk of infection, Thoen and LoBoe wrote in a journal commentary.