Obesity, respiratory disease and pulmonary infections

Obesity is one of the major epidemics of our time and its prevalence is only believed to increase over coming years. The detrimental effect of obesity on the risk of cardiovascular disease, diabetes and cancer has long been recognised and has subsequently impacted on public health policy across the globe. However, there are still gaps in our knowledge regarding the complex relationship between obesity, respiratory disease and infection. Obesity causes dysregulation of the immune system through mediation in various immune, metabolic and thrombogenic responses. However, the clinical impact of this immune dysregulation on the susceptibility, severity and outcome from various infections is still not clearly understood. Confounding aspects such as medical comorbidities, challenges in obtaining microbiology samples and invasive testing, issues with drug dosing and administration, and polypharmacy are probably also important in determining this risk in obese patients. The causal relationship between obesity and several respiratory diseases such as obstructive sleep apnoea (OSA) and obesity hypoventilation syndrome (OHS) is clear. However, the impact of obesity on the risk and outcome of respiratory infections, the infective complications in OSA and OHS, and the morbidity and mortality risk from infections in mechanically ventilated obese patients in the intensive care unit (ICU) setting is less well defined. Heterogeneity in study populations, differing methods of recording of weight and body mass index (BMI), variations in defining and reporting study outcomes and multiple confounding factors make for a disparity in study findings in this field that require further clarification. Large prospective cohort studies are needed to address many of the unanswered questions that remain.