Research is providing hints about the possible relationship between Clostridium difficile and various medications, according to studies recently presented in Washington, D.C., at the annual joint meeting of the American Society for Microbiology and the Infectious Disease Society of America.

C. difficile is one of the few conditions presently causing an increased number of deaths over time; it may contribute to as many as 20,000 deaths per year, according to the Centers for Disease Control and Prevention (CDC).

University of Iowa researchers reported that seasonal peaks in C. difficile occur mostly in March, following influenza peaks in December, January, and February. They note, "We believe that this relationship exists because of the increased antibiotic use during influenza seasons."

Christine Hansen and co-authors said that incidence of C. difficile fell dramatically with the institution of an antimicrobial stewardship effort. In 2004 and 2005, the Shands facility at the University of Florida put use restrictions on a number of antibiotics. During their four-year study, the consumption of ceftriaxone, ticarcillin/clavulanate, ciprofloxacin, gatifloxacin/levofloxacin, and clindamycin significantly decreased. The C. difficile rate fell from 1.4 to 0.8 cases per 1,000 patient days. The decrease was associated with reduction in the consumption of ticarcillin/clavulanate, gatifloxacin/levofloxacin, and clindamycin.

According to another paper presented at the Washington meeting, narcotic use may be increasing the severity of some C. difficile cases. Researchers looked at the records of 21,240 patients at St. Luke's Episcopal Hospital in Houston, of whom 123 developed C. difficile infection.

They found that 49.3 percent of patients who did not get C. difficile had been treated with narcotics and about 51.2 percent of those who did get the disease had not received narcotics. The gaps were much wider between patients with severe C. difficile and those whose cases were refractory.

The researchers, led by A. L. Mora, found that of C. difficile patients who had not been given narcotics, 40.4 percent had severe cases; of those who had received narcotics, 61.5 percent had severe cases. In addition, the researchers said, 20 percent of C. difficile patients who had received narcotics had refractory cases, defined as persistent diarrhea after seven days of treatment. Among the C. difficile patients who did not receive narcotics, only 10 percent of the cases were refractory. Researchers also found that use of narcotics appeared to increase the duration of time between admission and the diagnosis of C. difficile.

Another clue was offered by researchers associated with the Veterans Administration Connecticut Health Care System. They cautioned that some patients suspected of having C. difficile may actually have norovirus, even if there is no outbreak of that disease. Tests of stool samples of 73 patients suspected of having C. difficile showed that 9 had that disease, but 13 had norovirus and 51 had neither. The researchers noted that despite the advent of molecular assays for norovirus, testing for it is still relatively uncommon.

Also at the meeting, research from the Canadian Nosocomial Surveillance System Program, which can offer some studies not available in the United States, confirmed that severe C. difficile cases are more likely to be associated with the emerging NAP1/027/BI strain (known as NAP1) and are more likely to occur in the elderly. Of 1,008 C. difficile patients studied, 31 percent were infected with the NAP1 strain. Clifford McDonald, MD, a C. difficile expert from the CDC, indicated that the epidemic is still increasing, as far as can be determined from hospital discharge data through 2006. There are no regular reporting requirements for C. difficile.

KATHRYN FOXHALL is a healthcare journalist in the Washington, D.C., area.