In June 2015, an outbreak of Legionnaires’ disease in the Bronx section of New York City sickened 128 people and led to 12 deaths. It was the worst outbreak of Legionnaires’ in the city’s history, and one of the deadliest in the United States since the first recognized incidence of the disease, at the eponymous 1976 Legionnaires’ convention in Philadelphia. Public health authorities linked the Bronx outbreak to five cooling towers at a hospital and two hotels in the borough. The Bronx outbreak is part of an alarming trend. According to a CDC summary of outbreaks in North America, between 2000 and 2014 the incidence of Legionellosis, which includes both Legionnaires’ disease and Pontiac Fever, increased 286 percent, from 0.42 to 1.62 per 100,000 persons. These numbers are likely lower than the true incidence, since investigations of Legionnaires’ require an environmental assessment, which isn’t typically performed for cases that aren’t part of a recognized outbreak. One reason for Legionnaires’ high fatality rate—10 percent of all cases result in death, according to CDC—is the amount of time required to determine the source of an outbreak. Laboratories typically use a culture method to confirm the presence of bacteria, the species that causes most cases of Legionnaires’ disease, in a water-based sample. But grow slowly in culture, and results typically require 10 to 14 days, delaying remediation and increasing the likelihood that more people will be exposed. Increasingly, though, laboratories are using molecular analytical techniques that identify bacteria like much more quickly. Polymerase chain reaction, or PCR, is an analytical method that amplifies DNA in a sample and allows identification of a pathogen in a matter of hours. “PCR can be done a lot faster, and a lot more sensitively just based on the fact that sometimes with culture you get things dying in transit,” says Michael Saleh, the laboratory manager at Sporometrics in Toronto. This summer, Sporometrics was one of the first labs to be accredited under a new PCR field of testing (FoT) offered by AIHA Laboratory Accreditation Programs, LLC. During the 2015 Bronx outbreak, the bacteriology laboratory at the Wadsworth Center, which is affiliated with the New York State Department of Health, used PCR to analyze samples from seventeen cooling towers. Within 48 hours, building managers whose towers tested positive for were able to begin remediation, likely preventing further spread of the disease. However, both regulations and best practice still require culturing for , which labs typically perform according to ISO 11731:1998, , and the CDC publication . , so culturing is necessary to unequivocally confirm the presence of viable bacteria in a sample. Another advantage of culturing is that it allows public health authorities to link particular cases of disease with specific sources by comparing the cultured isolates at the strain level. According to the managers of several labs accredited by AIHA-LAP, the quick turnaround of PCR results makes it an attractive choice for industrial hygienists and other clients. And PCR’s usefulness extends beyond and other bacteria. A handful of labs offer PCR tests for a variety of molds, viruses, fungi, fecal indicators, and other hazards. “It’s pretty much unlimited what your targets can be with PCR,” says Ed Sobek, founder and president of Assured Bio Labs in Oak Ridge, Tenn., which has applied for AIHA-LAP accreditation in PCR. “If somebody’s interested in something, it’s pretty easy to whip up the assay, calibrate it, and get it going for the client. It’s very versatile in being able to cover the gambit of microbes that we’re dealing with.” PCR owes its versatility to the field of genetic sequencing. Knowing the sequence of DNA’s building blocks—the nucleotide base pairs adenine-guanine and cytosine-thymine, whose precise order determines whether an organism is a , an H1N1 virus, a spore of , or a human being—allows laboratories to develop highly specific tests that target unique regions of genetic code. A PCR test for fungi will target what is known as the ITS region of DNA; a test for bacteria will focus on the 16S region. There are two types of PCR analysis. The conventional method, known simply as PCR, is useful for identifying unknown organisms from a pure culture, a process known as “barcoding.” Conventional PCR will tell you what’s in the sample, but nothing else. If a client has a mixed sample and wants to know whether it contains a specific organism, the laboratory will use the quantitative variant of PCR, known as qPCR. “qPCR shines when you’re looking for something specific and you want to quantify it in a sample,” Saleh says. In April, Saleh, who serves on AIHA-LAP’s Analytical Accreditation Board, presented a webinar about PCR to an audience of site assessors to prepare them for visits to laboratories applying for accreditation in the PCR FoT.