New technology provides rapid diagnosis of respiratory illness
Georgia Regents Health System physicians now have a quick, thorough method to identify the viruses and bacteria causing respiratory illness.
Within an hour the technique, called polymerase chain reaction, determines which of 21 common viruses and bacteria are causing coughing, hacking, wheezing and other respiratory symptoms. That information tells physicians how best to treat – or not treat – the illness. It’s also giving physicians an accurate snapshot of circulating pathogens and when they occur.
“Our goal is to get patients the most rapid, accurate diagnosis,” said Dr. Christine M. Litwin, Medical Director of Clinical Microbiology and Immunology at GR Health System and Professor in the Medical College of Georgia Department of Pathology. “You don’t have to grow a virus, that takes days and we don’t always have days. You can go right to the molecular level to identify it and you don’t need much material to do that. PCR is very, very sensitive.”
PCR enables rapid copying of DNA, in this case found in a small nasal sample, to determine whether it’s the rhinovirus which causes the common cold, several different Variations of influenza virus or the new metapneumovirus that is making people sick. Since in the majority of respiratory viruses RNA actually carries the genetic information, it first converts RNA back to DNA.
“This is the wave of the future for more rapid diagnosis,” said Dr. Dennis L. Murray, Chief of the MCG Section of Pediatric Infectious Diseases.
At the Health System, most of the PCR testing is done in children age 5 and younger, who are most vulnerable to respiratory infections. The elderly, who may have multiple other medical conditions, are another vulnerable population.
“Children have many more viral infections than adults because kids get closer to each other,” Murray said. “They pass colds and other viral kinds of diseases around.” Young children also are more susceptible because their immune systems are less experienced than adults’ and not as prepared to fight an infection.
While there is not a proven treatment for every viral infection they can now detect, Murray notes in the case of viruses causing respiratory illness it can be as important to know what not to give: antibiotics, which are effective only against bacterial infections and are overprescribed in the United States. Overuse is hurting the effectiveness of the drugs when they are needed and, while use is finally trending downward, Murray says he regularly runs across cases of antibiotic resistance. There are conditions, such as certain pneumonias, caused by both a virus and bacteria, but in children pneumonia it’s usually viral, Murray said. Drugs such as Tamiflu, can diminish the duration and intensity of the flu. The kind of detail provided by PCR will become even more useful, as more therapies emerge, he said.
Despite the sophistication of the information generated, the PCR system is simple to use: the self-contained reagent pouch goes inside the machine, the hydrating solution goes in one side and the nasal sample goes in the other. Litwin notes its simplicity and rapidity dramatically improve lab efficiency.
The long-time standard has been growing a sample in culture for about three days, which requires virology skills to run and read and days to get results. It’s also limited in what it can find and some viruses and bacteria grow better in culture than others. Antigen tests also are available for certain pathogens, but also are not as rapid or as specific as PCR, which can reduce the need for multiple tests in a single patient.
Previously, for example, the lab could not diagnose the new metapneumovirus infection much less determine its incidence in the region, Litwin said. They also have numerous examples where the older tests produced negative findings while the more sensitive PCR was able to identify the infection type, she said.
PCR enables relatively inexpensive and rapid replication of DNA, making millions or even a billion copies available within a few hours rather than a few days. First used as a research tool, it’s moving into clinical settings to help diagnose divergent maladies such as cancer and genetic disorders.
For respiratory infections, GR Health System is using the FilmArray® Instrument, developed by BioFire Diagnostics, Inc., a spinoff biotech company of the University of Utah. Litwin, who came to MCG and GRU last year from the University of Utah where she was Medical Director of Microbial Immunology, worked to bring the PCR technology to Augusta. She is supplying BioFire Diagnostics with stool samples from area children as the company finalizes similar technology that can determine the source of diarrhea.