Some individuals exhale many more pathogen-laden droplets than others in the course of ordinary breathing, scientists have found, but oral administration of a safe saline spray every six hours might slash exhalation of germs in this group by an average 72 percent.

The researchers, at Harvard University and biotechnology firms Pulmatrix and Inamed, report results from their clinical study of 11 healthy males this week on the Web site of the Proceedings of the National Academy of Sciences. Their work may help decrease the spread of bacteria and viruses responsible for airborne infectious diseases such as influenza, tuberculosis, and SARS.

"We found a sharp demarcation between individuals who are ´high´ and ´low´ producers of bioaerosols, small droplets of fluid ex-haled from the lungs that may carry airborne pathogens," says lead author David A. Edwards, Gordon McKay Professor of the Practice of Biomedical Engineering in Harvard´s Division of Engineering and Applied Sciences. "Roughly half our subjects exhaled tens of bioaerosol particles per liter, while the other half exhaled thousands of these particles. The number of exhaled particles varied dramati-cally over time and among subjects, ranging from a low of one par-ticle per liter to a high of more than 10,000."

These results led Edwards and his co-authors to conclude that roughly half the population - six of 11 individuals in their study - may produce more than 98 percent of all potentially pathogenic bioaerosols.

The researchers found that a six-minute inhalation of aerosol-ized salt-water solution, often used in the treatment of asthma, can markedly reduce the number of bioaerosol particles exhaled by these "high-producers" for up to six hours. Using a cough machine designed to simulate normal human breathing, they linked the re-duction in droplet exhalation after saline administration to in-creased surface tension among fluids lining human airways, pro-ducing larger bioaerosol droplets that are less likely to remain air-borne and exit through the mouth.

"Administration of nebulized saline to individuals with viral or bacterial illnesses could dramatically reduce spread of these patho-gens without interfering with any other treatments," Edwards says. "This work could also point the way to new hygiene protocols in clinical settings as well as enclosed spaces."

It has long been known that exhaled bioaerosol particles con-stitute an important vector for the spread of infectious diseases, al-though the work by Edwards and colleagues is the first to suggest that a distinct subset of the human population is far more likely to spread pathogens via bioaerosols. Viruses known to spread from humans and animals through breathing, sneezing, and coughing in-clude those responsible for measles, influenza, foot and mouth dis-ease, chicken pox, bronchitis, smallpox, and SARS. Airborne bacteria include anthrax, Escherichia coli, Klebsiella pneumoniae, Francisella tularensis, and tuberculosis.

Edwards´ co-authors include Howard Stone in Harvard´s Divi-sion of Engineering and Applied Sciences; Edward Nardell at Harvard Medical School; Jonathan C. Man and Jeffrey P. Katstra at Pulmatrix; and Peter Brand, K. Sommerer, and Gerhard Scheuch at Inamed. The work was supported by Pulmatrix.