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Clostridioides difficile formerly Clostridium difficile (C. difficile) Surveillance

New Haven County
Data from the CT Emerging Infections Program's C. difficile surveillance program were presented at the International Conference on Emerging Infectious Diseases, March 2012.


Clostridioides difficile (formerly Clostridium difficile) is an anaerobic, spore-forming, gram positive bacillus that produces two exotoxins: toxin A and toxin B. The bacterium is ubiquitous in nature and able to survive for long periods in the environment. Transmission of C. difficile occurs primarily in healthcare facilities where environmental contamination by spores and exposure to antimicrobial drugs are common. Patients are 7-10 times more likely to get C. difficile infection (CDI) while taking an antibiotic or during the month afterwards. The primary risk factor for development of CDI in healthcare settings is recent antimicrobial use. Other risk factors include being 65 and older, a recent stay at a hospital or nursing home, a weakened immune system, a serious underlying medical condition, an intensive care unit (ICU) admission, extended hospital stays, and having a previous CDI episode.

CDI has increased in incidence and severity, becoming the most common pathogen of healthcare-associated infections (HAI) and is a well-known cause of antibiotic associated diarrhea (AAD) and colitis. CDI accounts for 15 to 25% of all episodes of AAD. CDI causes almost half a million infections and estimated 29,300 deaths in the United States each year. About 1 in 6 patients who get CDI will get it again, in the subsequent 2-8 weeks. More than 80% of CDI related deaths occur in people 65 and older. CDI costs the health care system an estimated $3.2 billion annually. Healthcare facilities are strongly recommended to have antibiotic stewardship protocols and infection control practices in place to reduce the incidence of CDI.

Commonly considered to be hospital-acquired, rates of community-associated (CA) CDI have been increasing and currently make up more than 50% of cases reported. The sources of CA-CDI and the risks for developing CDI in community populations were previously thought to be low risk and are not well defined. Given the emergence and increasing significance of CA-CDI in public health, it is important to understand how poverty may influence the risk of CA-CDIs to improve not only the overall understanding of CDI epidemiology but also develop potential interventions that might be implemented at the community level.


The Connecticut EIP C. difficile surveillance project monitors the incidence of healthcare (HA) and community-associated (CA) CDI at the population level, tracks changes over time, identifies at-risk populations, estimates disease burden and social determinants of health inequity. The Connecticut EIP collaborates with nine other EIP sites and CDC to characterize C. difficile strains responsible for CDI in the population under surveillance with a focus on strains from community-associated cases; and describes the epidemiology of CDI and generates hypotheses for future research activities. Ultimately, these efforts may provide healthcare facilities and providers with valuable guidance leading to an overall decline in CDI incidence.


Throughout 2009-2023, the Connecticut EIP CDI surveillance project used New Haven County as its catchment area. In June 2022, the United States Census Bureau approved a request from the State of Connecticut to adopt the state’s nine planning regions as county-equivalent geographic units to collect, tabulate, and disseminate census data. The catchment area for CDI surveillance beginning in 2024 will be South Central and Naugatuck planning regions. This catchment area has a population size of 1,019,904 residents, representing 28% of the state’s population. CDI surveillance does not use the entire state because the quantity of cases reported would not allow for high quality surveillance activities to be performed. This catchment area is demographically diverse with an estimated 63% of the population White, 19% Hispanic, and 14% Black. It is comprised of urban, suburban, and rural locations.

A list of all positive C. difficile tests will be evaluated to determine if in catchment and classification. A case is classified as community-onset if the C. difficile-positive stool was collected as an outpatient or within 3 days of hospital admission. A case is classified as healthcare-facility onset (HCFO) if it was a hospital-onset CDI (positive stool was collected >3 days after hospital admission) or a long-term care facility (LTCF) onset CDI (positive stool collected in a LTCF or from a LTCF resident admitted to a hospital). Community-onset cases are further classified as community-associated if there was no documentation of admission to a healthcare facility in the preceding 12 weeks; all other community-onset cases are considered community-onset healthcare-facility associated (CO-HCFA). Both the CO-HCFA cases and all HCFO cases are further classified as healthcare-associated CDI.

Each presumptive community-associated (CA) case, each community-onset healthcare associated (CO-HCFA) case, and a 10% sample of health-care onset (HCFO) cases will require a full chart review to complete the case report form. Select laboratories will save stool samples on cases of CDI for further laboratory evaluation including culture and toxinotype testing.

Recent Publications

Centers for Disease Control and Prevention - Clostridium difficile Tracking

Centers for Disease Control and Prevention: Deadly Diarrhea: C. difficile Causes Immense Suffering, Death

Healthcare-Associated Infections-Community Interface Data Visualization Tool (HAICViz)

Project Contact

Danyel Olson, MPH
Project Coordinator
Connecticut Emerging Infections Program
One Church Street, 7th floor
New Haven, CT 06510

Clostridioides difficile (C.difficile) Surveillance Staff

  • Maria Correa
  • Anisa Linton
  • Julia Ellman