Extra Weight Linked with Increased Survival in Some Patients with Infectious Diseases

The results of 2 studies presented at the European Congress on Obesity in Vienna, Austria May 23-26, 2018, indicate that patients who are overweight or obese have better mortality outcomes than patients who are at a normal weight when it comes to fighting off infectious diseases.

For the first study, investigators led by Professor Shy-Shin Chang and Dr Yu-Jiun Lin, Taipei Medical University Hospital, Taipei City, Taiwan, and Dr Jon Wolfshohl, Department of Emergency Medicine, John Peter Smith Hospital, Fort Worth, Texas, and colleagues, used the Nationwide Readmission database of the United States from 2013 to 2014 to analyze patient data from over 1000 US hospitals. The goal of the study was to determine the impact of being overweight or obese on patient outcomes for pneumonia.

Approximately 1.7 million episodes of pneumonia were analyzed. According to a news release on the study, “a pneumonia-associated hospitalization was defined as one in which the discharge record listed a principal diagnosis of pneumonia or a secondary diagnosis of pneumonia if the principal diagnosis was respiratory failure or sepsis. Use of mechanical ventilation was used to stratify pneumonia of different severity. Hospitalized pneumonia patients were categorized into normal (body mass index [BMI] under 25), overweight BMI between 25 and 30), and obese (BMI over 30).” The team used propensity score-matched analysis to “minimize baseline differences between patients with different body weights.”

A total of 1,690,760 episodes of pneumonia hospitalization were included in the study, of which, 17,992 patients were overweight, 195,889 were obese, and 1,476,879 were of normal weight. The results indicated that obese patients were 29% more likely to survive than normal-weight patients (without ventilator use), and overweight patients were 23% more likely to survive. In patients with severe pneumonia (with ventilator use), obese patients were 30% more likely to survive and overweight patients were 21% more likely to survive. Of note: across all subgroups, those patients with a lower comorbidity burden/severity were more likely to survive.

Professor Chang advised Contagion® that a limitation of the study is that it "cannot completely overcome covariates, although they used propensity score matching to minimize imbalance among normal weight, overweight, and obesity groups." He cautioned that "the obesity paradox exists in acute illness; however, long-term survival is decreased in patients who are obese."

The second study was carried out in Denmark and was led by Sigrid Gribsholt, Aarhus University Hospital Department of Clinical Epidemiology, Denmark, and colleagues. In their study, Dr. Gribsholt’s team “identified 35,406 individuals with an incident acute medical or surgical inpatient admission for an infectious disease during 2011 through 2015 in the Central Denmark Region,” according to a news release on the study. Dr. Gribsholt shared with Contagion® that the team, "included all types of infectious diseases, but performed separate analyses on pneumonia, urinary tract infection, and sepsis. About 52% of the patients were male and the median age was 61 (interquartile range 46-77)." In terms of comorbidities, 58% of the patients had no hospital-diagnosed co-morbidities, 29% had a moderate degree of comorbidities, and 13% had a high degree of comorbidities.

Although the team did not examine race, Dr. Gribsholt advised that the majority of the patients were white.

The risk of death within 90 days after discharge in association with a patient's weight was examined, using normal weight as a reference. According to the news release, the team, "adjusted for potential confounding factors, and examined the influence of recent weight change, comorbidities, cancer, and tobacco smoking on the association between BMI and mortality.”

The investigators found that the adjusted risk of death following an infection was 2.2 times higher in patients who were underweight than those of a normal weight. Conversely, those patients who were overweight or obese were 40% and 50%, respectively, less likely to die after an infection than those of normal weight. Furthermore, “patients with obesity, presence or absence of recent weight changes, comorbidities, cancer, or smoking had little effect on the association with decreased mortality,” according to the news release.

Some limitations of the study, according to Dr. Gribsholt were that, "Smoking was self-reported by the patients and that comorbidities may lead to weight loss before patients are diagnosed in a hospital which may not be captured in our study. Patients with obesity have a high mortality due to other diseases, which may influence our results. Doctors may have a lower threshold to admit patients with obesity which may lead to admission with less severe infections."

Furthermore, Gribsholt cautioned, "it is possible that obesity may have a protective effect in acute infection; however, in the general population, obesity is associated with high mortality, Thus the protective effect in an acute infection may not outweigh the overall risk. Furthermore, we found a high mortality associated with those patients who were underweight, which may be important in a clinical setting."