Respiratory Tract Infections: Introduction

00:01 The subject of this lecture are lung infections and particularly pneumonia. The lung is exposed to the environment continually, and there are two main forms for that, one is through the inhaled air that we will breath in every day, repeatedly and the other is that is actually connected to the upper respiratory tract, and the upper respiratory tract is colonized heavily with bacteria and this means that the lungs are continually bombarded with microbial pathogens of different sorts. Through inhaled air it will breath in infected droplets from people who are sneezing or coughing who are infected with viruses, mycoplasma, chlamydia or tuberculosis, and in addition, there are fungal spores which are pretty ubiquitous in the atmosphere, and will be breathed in when you breathe normally.

00:48 Bacterial pathogens tend to come from the back of the throat, so they are part of the normal commensal flora living in the pharynx and the upper respiratory tract, and they get into the lung by microaspiration. Small droplets of the secretions from the upper respiratory tract make their way past the larynx, down into the lungs, and could potentially cause infection. However, because of our normal immune mechanisms the lungs, generally speaking, are kept sterile despite this constant bombardment of microbial organisms. But those immune mechanisms do break down and infections are common, and in fact, three of the most are common pathogens causing infections across the world, and causing death due to microbial infection across the world, are due to respiratory tract infections, Mycobacterium tuberculosis, Influenza A, those are the subject of another talk on lung infections, and Streptococcus pneumoniae. Now, Streptococcus pneumoniae is the commonest cause of pneumonia and is estimated to kill about 3 million people per year across the globe and about 85% of those due to pneumonia. When we are talking about lung infections,