CAP TODAY Pathology/Laboratory Medicine/Laboratory Management
Ann Griswold, PhD
May 2014—Modern health care is more advanced than ever, but institutions continue to battle one problem that refuses to go away: hospital-acquired infections. They should be preventable, yet a recent CDC report estimates that one in 25 U.S. patients acquired at least one infection during a hospital stay in 2011. The most pervasive nosocomial pathogens, by far, are Clostridium difficile and Staphylococcus aureus (Magill SS, et al. N Engl J Med. 2014;370: 1198–1208).
“Hospital-acquired infections are infections that are not supposed to happen,” says Larry Massie, MD, chief of Pathology and Laboratory Medicine for the New Mexico VA Health Care System and a professor of pathology at the University of New Mexico. “This is even more relevant now that the Centers for Medicare and Medicaid Services don’t reimburse for certain hospital-acquired infections. That’s putting a lot of pressure on hospitals to control this problem because they’re not recovering the expenses they incur.”
In a recent Q-Probes study, “Microbiology Testing for Hospital Infection Control,” Dr. Massie and colleagues report the isolation and detection rates of toxigenic C. difficile and methicillin-resistant S. aureus at 41 institutions in the United States and four facilities abroad. The results shed light on surveillance practices and detection techniques that can help health care facilities edge closer to the goal of eradicating nosocomial infections.
“We wanted to see how these two important nosocomial infections were being detected in the laboratories and how the laboratory evidence was being put to use. In this case, the clinical microbiology laboratory is the pivot on which the detection and the management of these infections turn,” notes Frederick A. Meier, MD, an author of the Q-Probes study and senior staff pathologist at Henry Ford Hospital in Detroit and director of regional pathology services, Henry Ford Health System.
To collect data for the study, the authors asked participating institutions to track at least 30 MRSA isolates, or all MRSA isolates identified during a 60-day period, whichever came first. The participants then sorted through the isolates to find true nosocomial infections, defined as those acquired at least two days after hospital admission. Surveillance specimens—those routinely collected from patients prior to or within 48 hours of admission and found to be positive—were distinguished from clinical specimens, collected from patients more than 48 hours after admission in response to signs of infection.
The study’s participants calculated the turnaround times from specimen collection to result reporting, and noted the detection methods. In the second part of the study, a similar process was repeated for isolates of toxigenic C. difficile. The information was used to calculate the surveillance detection rates, the clinical detection rates, and the overall detection rates for each organism.
Several unexpected findings emerged, the authors note. Most notably, the detection rates calculated in the Q-Probes study differ from those in the recent CDC report, which found that C. difficile accounted for 12.1 percent of all health-care–associated infections while S. aureus, including MRSA, accounted for 10.7 percent.
Dr. Meier
“At least in our little population, we found a higher median infection rate with MRSA than with C. difficile, with rates of 15 percent and eight percent, respectively,” Dr. Meier says. “These overall detection rates are valuable for people who are wondering about the institutional investment that needs to be made in testing and molecular tools.”
Fewer than half of the hospitals in the study used molecular tools to amplify the MRSA mecA gene, while most hospitals used bacterial culture to detect the pathogen. Predictably, the use of nucleic acid amplification allowed for much faster median turnaround times. Turnaround times were further reduced in laboratories with 24/7 testing capabilities.