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Microbiology
Respiratory System Infections

Respiratory System Infections

Side-profile photo of a red-haired, bearded man wearing glasses, mouth open mid-sneeze, with a visible spray of fine droplets bursting forward from his mouth against a black background.
Aerosols produced by sneezing, coughing, or even just speaking are an important mechanism for respiratory pathogen transmission. Simple actions, like covering your mouth when coughing or sneezing, can reduce the spread of these microbes. (credit: modification of work by Centers for Disease Control and Prevention)

The respiratory tract is one of the main portals of entry into the human body for microbial pathogens. On average, a human takes about 20,000 breaths each day. This roughly corresponds to 10,000 liters, or 10 cubic meters, of air. Suspended within this volume of air are millions of microbes of terrestrial, animal, and human origin— including many potential pathogens. A few of these pathogens will cause relatively mild infections like sore throats and colds. Others, however, are less benign. According to the World Health Organization, respiratory tract infections such as tuberculosis, influenza, and pneumonia were responsible for more than 4 million deaths worldwide in 2012 (World Health Organization, “The Top Ten Causes of Death,” May 2014).

At one time, it was thought that antimicrobial drugs and preventive vaccines might hold respiratory infections in check in the developed world, but recent developments suggest otherwise. The rise of multiple-antibiotic resistance in organisms like Mycobacterium tuberculosis has rendered many of our modern drugs ineffective. In addition, there has been a recent resurgence in diseases like whooping cough and measles, once-common childhood illnesses made rare by effective vaccines. Despite advances in medicine and public health programs, it is likely that respiratory pathogens will remain formidable adversaries for the foreseeable future.

Sections

  • Anatomy and Normal Microbiota of the Respiratory Tract — the major anatomical features of the upper and lower respiratory tract, the normal microbiota of each region, the defenses that respiratory- tract membranes mount against microorganisms, and how microbes overcome these defenses to cause infection, along with the signs and symptoms of respiratory infection and the risk that smoking poses for pneumonia.
  • Bacterial Infections of the Respiratory Tract — the bacterial causes of respiratory disease, including streptococcal infections and their sequelae, acute otitis media, bacterial rhinosinusitis, diphtheria, the varieties of bacterial pneumonia (pneumococcal, Haemophilus, Mycoplasma or walking pneumonia, chlamydial pneumonias and psittacosis, health care–associated pneumonia, and Pseudomonas pneumonia), tuberculosis, pertussis (whooping cough), Legionnaires disease, and Q fever.
  • Viral Infections of the Respiratory Tract — the common cold, influenza and the risk of flu pandemics, viral pneumonia, SARS and MERS, and the viral respiratory diseases that produce skin rashes: measles, rubella, and chickenpox and shingles.
  • Respiratory Mycoses — the fungal diseases of the respiratory tract, including histoplasmosis, coccidioidomycosis, blastomycosis, mucormycosis, aspergillosis, Pneumocystis pneumonia, and cryptococcosis.

This chapter is adapted from Microbiology, Chapter 22: Respiratory System Infections by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster, and OpenStax, © OpenStax, licensed under CC BY-NC-SA 4.0. Access the original for free at openstax.org. Each section page records its own changes from the source. Changes: the chapter-opening figure is the source’s photo of a man sneezing, re-encoded for the web, with its alt text rewritten to describe what is actually visible; the module’s footnote is rendered as an inline parenthetical citation after the sentence it supports, with its bare access URL dropped; the module defines no terms.

Protozoan and Helminthic Infections of the Skin and EyesAnatomy and Normal Microbiota of the Respiratory Tract