MOST OF the tuberculosis bugs spread between people during recent outbreaks in Cork and Kerry can be traced back to the days when the disease was prevalent in Ireland and are not, contrary to common perception, being brought into the country by foreign nationals.
This is according to a survey carried out by the Department of Microbiology at Cork University Hospital, which looked at strains stored from TB samples taken in 2004-2006, as well as from an outbreak which affected two Cork creches in 2007, using new DNA techniques.
Professor of medical microbiology at UCC and consultant microbiologist at CUH, Michael Prentice, said advances in DNA sequencing now allowed scientists to tell the difference between closely related bacteria that were previously indistinguishable.
“Using DNA techniques, we can see that most of the tuberculosis bacteria spread between people in Cork and Kerry are local strains presumably persisting from the days when tuberculosis was common,” he said.
The outbreak among pupils at a Cork primary school in August of this year was not included in the survey.
The results of the survey, recently published in the journal , Infection, Genetics and Evolution, suggest the strains that spread in the Cork and Kerry areas – including the Cork creche outbreak in 2007 – are of Euro-American lineage and are mostly local strains of the bacteria.
According to Prof Prentice, who will be one of the keynote speakers at a public health forum on TB at UCC on November 9th: “While none of the strains associated with other countries seem to be spreading in our population, this does not mean that they can’t spread, and we want public health to be quite alert to ensure that these strains do not spread as some of them tend to be more drug resistant.”
Meanwhile, separate Irish research just published has shown smokers who contract tuberculosis can infect other people for longer than non-smokers. Researchers from St James’s Hospital and Trinity College Dublin said there could be an increased public health risk as a result. All 160 patients with TB of the lung who attended St James’s between April 2007 and April 2008 were looked at. The aim of the study was to see whether smokers who were receiving anti-TB treatment were more likely to be infectious to others.
Non-smoking TB patients are generally infective for about six weeks after they commence treatment. After excluding certain patients, including those with drug-resistant tuberculosis and those whose sputum tested negative for the bacteria, the researchers found that those with a history of smoking were about four times more likely to remain infectious than others who were also on treatment, but who did not smoke.
Writing in the current issue of the Irish Medical Journal, the authors say: "The consequences of a prolonged infectious interval include an increased public health risk of spreading the epidemic, and prolonged isolation of the TB patient." They postulate that the immune system suppression action of nicotine may have a role to play in the finding.
Between 400 and 500 new TB cases are identified here every year.