Medical researchers are warning there is a strong link between the smoking of marijuana waterpipes or bongs and the spread of tuberculosis.

Doctors in the Hunter New England area in New South Wales made the link when three young, Australian-born patients who were also heavy marijuana users were diagnosed with TB.

Tests conducted on associates of the infected patients found there was a six-fold increase in the chance they had contracted latent TB.

Dr Michael Hayes, from the Calvary Mater Hospital in New South Wales, says a fourth person of the same demographic has presented since the research was completed.

"Pulmonary tuberculosis occurs most frequently in people who were born overseas... so it is unusual to see it in young Australian born, non-Indigenous patients. There is a higher rate in Indigenous communities," he said.

He says the research could be helpful to physicians across the country.

"To think of pulmonary tuberculosis as a possible diagnosis because often a persistent cough might otherwise be dismissed in this demographic as just a bronchitis from a smoking as such," he said.