Respiratory infections: a global burden

Respiratory infections are accountable for significant morbidity, and mortality world-wide. Amongst all diseases, lower respiratory tract infections have the greatest burden on human health, with a two and six-fold greater disability-adjusted life years compared to ischaemic heart disease and diabetes mellitus, respectively. Not only do pathogens cause primary respiratory infection such as pneumonia, but they also play a paramount role in the exacerbations of chronic lung diseases such as chronic obstructive pulmonary disease, interstitial lung disease and bronchiectasis. Lower respiratory tract infections, excluding tuberculosis, are the third biggest global killers, responsible for 3.2 million deaths in 2015. Importantly, in low-income countries lower respiratory tract infections remain the top cause of death. This is linked to poverty, which is associated with malnutrition, overcrowding, and air pollution, which increases the risk of infection with airborne pathogens. The majority of these infections are avoidable, but due to a lack of resources and access to healthcare people do not have access to immunisations or get timely antibiotics. In this setting, the enormous burden of human immunodeficiency virus (HIV) infection augments the risk of infections with common, as well as, opportunistic respiratory pathogens. In contrast, in high-income countries, there is better access to immunisations and medications, but an ageing population, increased prevalence of chronic lung disease and iatrogenic immunosuppression are driving the incidence of respiratory infections. It is estimated that by 2050, 2 billion of the world’s population will be older than 65 years and >1 billion people will have a preventable chronic lung disease and unless respiratory infections can be prevented in these at-risk groups, healthcare systems will not cope with the disease burden. Furthermore, modern treatments for chronic inflammatory/autoimmune disease and cancer with drugs that impact on immunity to pathogens has led to the appreciation of the increased risk of acquiring respiratory infections amongst these individuals. Importantly, we are living in an era where antibiotics that previously were efficacious are no longer effective due to the increasing presence of drug-resistance pathogens, and new antibiotics are taking too long to come through the pipe-line. Even in the presence of effective anti-microbial therapy multi-morbidity and mortality is still unavoidable for many patients with severe infections due to the exaggerated host response and bystander tissue injury. Therefore, although there is more control over the spread of communicable diseases and improvements in supportive care for critically ill patients, the impact of respiratory pathogens on human health remains so great that we must not stop our journey to better understand host-pathogen interactions and identify novel preventative and therapeutic strategies