The respiratory microbiome and respiratory infections.

Despite advances over the past ten years lower respiratory tract infections still comprise around a fifth of all deaths worldwide in children under five years of age with the majority in low- and middle-income countries. Known risk factors for severe respiratory infections and poor chronic respiratory health do not fully explain why some children become sick and others do not. The respiratory tract hosts bacteria that can cause respiratory infections but also normal commensal bacteria. Together, this microbial population is called the microbiome. The composition of the respiratory microbiome in the first few months of life is likely influenced by external factors such as environment, mode of delivery and infant feeding practices, which are also associated with susceptibility to respiratory infections and wheezing illness/asthma. Recently, multiple studies have shown that respiratory microbiota profiles early in life are associated with an increased risk and frequency of subsequent respiratory infections, disease severity and occurrence of wheeze in later childhood. Early interactions between infectious agents such as viruses and the respiratory microbiome have shown to modulate host immune responses potentially affecting the course of the disease and future respiratory health. Deeper understanding of these interactions will help the development of new therapeutic agents or preventive measures that may modify respiratory health outcomes and help us to stratify at risk populations to better target our current interventional approaches.