CHICAGO — The “D test” is a critical second-step test when methicillin-resistant Staphylococcus aureus cultures come back showing erythromycin resistance and clindamycin susceptibility, according to Dr. Jeffrey Starke.
“It should be automatic—every hospital in the country should know about this test. If you are not running it, you have to start,” cautioned Dr. Starke, professor and vice chairman of pediatrics at Baylor College of Medicine, Houston.
As the number of methicillin-resistant Staphylococcus aureus (MRSA) infections has escalated to epidemic proportions at Texas Children's Hospital, discordance in the bacteria's response to erythromycin and clindamycin has become a red flag for the organism's potential to develop “inducible resistance” to clindamycin, Dr. Starke said at a meeting sponsored by the American College of Emergency Physicians.
“If it's erythromycin and clindamycin susceptible initially, or resistant to both initially, there is no issue,” he explained. “But it's when there is discordance—when it shows erythromycin resistance but clindamycin susceptibility—that this test needs to be done.”
The clindamycin disk induction test, or D test, will determine if the organism is truly susceptible to clindamycin or if there is a risk of inducible clindamycin resistance, he said.
“When an isolate has inducible clindamycin resistance, treatment failures often occur when clindamycin is used—especially if the infection is serious or deep-seated,” Dr. Starke said.
The current epidemic of community-acquired MRSA infection differs from the traditional disease in terms of both the risk factors and the aggressiveness of the infection, he said.
“Patients are almost exclusively normal hosts,” he said, listing current risk factors as race (African Americans have significantly increased risk, compared with whites), prior infections, infected household contacts, day care, and competitive athletics.
Unlike the traditional MRSA involvement of skin and soft tissue (and sometimes muscle, bone, or joints), current infections can involve all these areas simultaneously and continue to progress. “We are seeing a large number of complicated necrotizing pneumonias and empyemas, we are seeing S. aureus meningitis, sepsis, and septic venous thrombosis,” he said. “If you are not seeing this yet, it is coming,” he warned.
In the case of such deep, acute involvement, the role of surgical intervention is equal to, if not more important than, that of antibiotics, Dr. Starke emphasized.