A new study looked at Clostridioides difficile infection (CDI) in outpatient settings and found the bacteria may be underdiagnosed, according to a study out Jan. 11 in Open Forum Infectious Diseases.

Researchers from Kaiser Permanente Southern California and Kaiser Permanente Northwest looked at two large integrated health systems. The team evaluated 777,533 medically attended diarrhea (MAD) episodes that occurred in 592,877 people between 2016 and 2021. The researchers focused on MAD because little is known about them, and they’re thought to contribute to a slew of undiagnosed CDI cases because these patients don’t always get tested for CDI.

Stool specimens were ordered for 37% of the samples, though only 12.1% of people had tests for CDI. Tests were most frequent in those ages 70 and up, and less common for the 18- to 49-year old crowd. 

The rate of CDI on an outpatient basis was 51.0 per 1,000 patient-years over the entire study period. It fell 58.2 in 2016 to 45.7 in 2021. Incidence went up with age and was the highest among women, non-Hispanic White patients and people with underlying comorbid conditions. CDI, which can be deadly, is prevalent in nursing home settings. 

Of the outpatient CDI cases, 84.1% were community associated; that is the person wasn’t hospitalized 12 weeks before the case; 44.1% of the people took an antibiotic within 30 days of the case being reported. About one-third of patients with outpatient CDI didn’t receive treatment or have frequent contact with the healthcare system in the year after their infection.

The lack of recent antibiotic use or hospitalization among many of the people with CDI cases indicates that household transmission could be contributing to the infection in the general community, the team wrote.

“While lower-than-expected rates of CDI treatment and relatively low levels of healthcare utilization in the one year following outpatient CDI diagnosis indicate short illness duration and limited impact on the healthcare system, the low frequency of C. difficile testing among patients presenting with diarrhea indicates that outpatient CDI may be underdiagnosed, and the incidence of outpatient CDI may be higher than appreciated,” the authors wrote.

The authors add that the lack of recent antibiotic use or hospitalization among many of the identified outpatient CDI cases suggests other factors, such as transmission within households, could be contributing to the occurrence of CDI in the general community.