The scent of an illness

Just as the human nose interprets a whiff of smoke as a warning of fire, electronic noses can detect the unique “scent signatures” of diseases, from bacterial infections to lung cancer.

Consisting of arrays of chemical sensors, these high-tech noses distinguish the breath, urine and blood of the sick from those of the healthy. Most devices are still in the experimental stages, with some being tested on patients with suspected pneumonia and other lung diseases, sinus infections, diabetes and cancer. The technology could screen and diagnose diseases and monitor any recurrence right in the doctor’s office or at the patient’s bedside.

“What you’re seeing is the emergence of the technology to be a diagnostic tool,” said Steve Sunshine, chief executive of Cyrano Sciences in Pasadena, which makes an electronic nose undergoing tests at several medical centers.

The practice of diagnosing illness through breath smells dates at least to Roman times, when doctors called the musky breath of kidney failure patients fetor hepaticus. Doctors today liken the distinctive breath of diabetics with dangerously high blood sugar to the scent of a popular brand of chewing gum.

In the last few decades, scientists worldwide have been developing ways to detect the chemical signatures of food spoilage, pollution and biological attacks, and several teams have been zeroing in on medical applications. Because diseases create distinct changes in the gases we exhale and in the gases emitted by bacteria infecting our blood and urine, electronic noses can be programmed to sense their chemical signatures.

So far, only one electronic nose has been approved in this country for commercial use. In November 2001, the U.S. Food and Drug Administration said Osmetech of Crewe, England, could market the Osmetech Microbial Analyser for detecting the urinary tract infections that plague millions of Americans each year. The device, based on technology developed at the University of Manchester, analyzes gases from bacteria in urine within hours; bacterial cultures take days.

In January of this year, Osmetech announced that the device had also been approved for diagnosis of bacterial vaginosis. Using vaginal fluids, it distinguishes bacterial vaginosis, an infection linked to miscarriage and premature delivery, from other common vaginal infections.

A team of Caltech researchers was among pioneers of electronic noses. Its device uses chemical sensors made of special polymers, which change electrical resistance when they come into contact with gases. Computers identify the gases by the patterns of electrical changes. The team has formed Cyrano Sciences Inc., which pairs chemical sensing and interpretation in an $8,000 device dubbed Cyranose, named after Edmond Rostand’s “Cyrano de Bergerac,” the 1897 play about a character with an enormous nose. Sunshine said his company is about a year from seeking FDA approval to market its device for medical purposes.

On Sunday, researchers from the Cleveland Clinic reported at the American Thoracic Society meeting in Seattle that the Cyranose had differentiated the breath of 14 lung cancer patients from that of 20 healthy people and 25 patients with other lung ailments. (Their presentation followed a May 10 report in New Scientist magazine that an electronic nose developed at the University of Rome accurately picked out 35 cases of lung cancer from among a group of 60 hospital patients and was easier on patients than bronchoscopy, which involves inserting a lighted tube into the lungs).

Electronic noses have also shown great promise in screening for pneumonia. Last November, researchers at the University of Pennsylvania reported that Cyranose accurately and quickly detected pneumonia cases when used on 415 critical-care patients on ventilators. The device speeds treatment by distinguishing quickly between viral or bacterial pneumonia.

“It will save money by preventing unnecessary prescription of antibiotics and by catching the disease earlier in its course,” said lead author Dr. C. William Hanson III, a Penn anesthesia professor who said he foresees using the device more widely in a year or two. He said Cyranose could reduce unnecessary antibiotic use that contributes to resistance.

In other studies, Dr. Erica Thaler, an ear, nose and throat specialist at Penn, has used Cyranose to pinpoint which cases of sinusitis require antibiotics. She also has found that the device can distinguish between drainage of normal nasal fluids and the dangerous leakage of spinal fluid, which requires immediate attention.