Rates of infection with the deadly superbug Clostridium difficile were highest in the Northeast region of the country and in the spring season over the last 10 years, according to a new study.

Researchers from the University of Texas retrospectively analyzed 2.3 million cases of Clostridium difficile infection (CDI) from 2001-2010 and found the highest incidence in the Northeast (8.0 CDI discharges/1000 total discharges), followed by the Midwest (6.4/1000), South (5.0/1000), and the West (4.8/1000).

Seasonally, spring had the most cases (6.2 CDI discharges/1000 total discharges), followed by winter (5.9/1000), summer (5.9/1000) and fall (5.6/1000). Adults and older adults followed overall trends, whereas pediatric CDI was highest in winter.

CDI mortality was highest in the Midwest (7.3 percent) and among older adults (9.0 percent).

“The peak incidence in the spring could be attributed to increased utilization of antibiotics in winter months,” the authors state. “Prior studies have found a 1 to 2 month lag time between antibiotic exposure and the development of CDI.”

C. difficile causes inflammation of the colon and life-threatening diarrhea. According to the CDC, C. difficile has become the most common microbial cause of healthcare-associated infections in U.S. hospitals and costs up to $4.8 billion each year in excess healthcare costs for acute care facilities alone.

The CDC estimates that C. difficile caused almost half a million infections in 2011 and that 29,000 U.S. patients died within 30 days of their initial diagnosis.

Citation: “Regional and seasonal variation in Clostridium difficile infections among hospitalized patients in the United States, 2001-2010,” by Jacqueline R. Argamany, Samuel L. Aitken, Grace C. Lee, Natalie K. Boyd, and Kelly R. Reveles, American Journal of Infection Control, Volume 43, Issue 5 May 2015.