Low Body Weight Heightens CDI Risk in Elderly Population


In a study of more than 600 elderly Japanese, being overweight was a protective factor against Clostridioides difficile infection (CDI).


A new study examining older Japanese patients with pneumonia shows people with a low body mass index (BMI) are at an increased risk of Clostridioides difficile infection (CDI).

On the other hand, the study showed that patients with high BMI do not appear to be at higher risk of CDI. The findings were published in the journal Geriatrics & Gerontology International.

Corresponding author Kiyohide Fushimi, MD, PhD, of the Tokyo Medical and Dental University, and colleagues, explained that CDI can be a devastating disease in elderly patients, with a high mortality rate and significant hospital stays for those who survive. Some existing research has linked high BMI with CDI risk, but the investigators said no such research has been conducted within an Asian population. There is reason to believe outcomes in Asian countries could be different, they said, in part because the countries tend to have lower rates of obesity than many western countries.

Fushimi and colleagues set out to discover whether BMI and CDI appeared to be linked among a medically fragile group, those over the age of 65 who were hospitalized with pneumonia. They retrospectively examined a cohort of 221,242 patients with pneumonia who were hospitalized between July 2014 and March 2016.

The authors found that 611 of the patients eventually developed CDI. When they analyzed those patients based on BMI, the investigators found patients with BMIs under 18.5 kg/m2 were more likely to be diagnosed with CDI (odds ratio [OR] 1.38, 95% confidence interval [CI] 1.17-1.62), than patients with “normal” body weight: BMIs ranging from 18.5-24.9 kg/m2.1

The authors said there are several possible reasons lower BMI appeared to be problematic with regard to CDI risk.

“Low BMI might reflect poor nutritional status, leading to impaired immune response, which could result in a higher risk for CDI,” they wrote.

In addition, they said, it could also be because patients with low BMI have lower skeletal muscle mass.

“Skeletal muscle plays an anti-inflammatory and immunoprotective role by producing myokines, and potentially reduces age-related multimorbidity,” they wrote.

Notably, patients who were overweight were not at a higher risk of CDI. In fact, they had a lower risk (OR 0.63, 95% CI 0.45-0.8) than patients with normal body weight.

“This could be in line with the ‘obesity paradox,’ which refers to the idea that obesity has favorable effects on disease prognosis,” Fushimi and colleagues wrote. “Despite the fact that obesity is a risk factor for many diseases, obese patients have been reported to have a favorable prognosis in cases of heart failure, diabetes mellitus, cancer and chronic obstructive pulmonary disease.”

The study also showed that male sex was a risk factor for CDI. The investigators said many previous studies have found sex does not play a role in CDI risk. They said the issue warrants further study.

The authors said given the prevalence of adverse outcomes among elderly patients with CDI, clinicians should be aware of patients who might be at a higher risk of the infection.

“[The present study] might also support the importance of maintaining healthy body weight and skeletal muscle mass in preventing or treating older patients with pneumonia, as suggested in other studies,” they concluded.


1. Suzuki R, Sakata N, Fushimi K. Association of body mass index with Clostridioides difficile infection among older patients with pneumonia in Japan [published online ahead of print, 2021 Dec 1]. Geriatr Gerontol Int. 2021;10.1111/ggi.14316. doi:10.1111/ggi.14316

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