Introduction to Microbial Disease: Pathophysiology and Diagnostics

Infections are a major cause of morbidity and mortality worldwide. Only a fraction of microorganisms are recognized as primary human pathogens as a result of their having abilities to attach to and/or enter human cells, produce toxins, and/or evade the host immune system. By comparison, commensal organisms in the human microbiome are essential for human health. Pathogenic organisms may be acquired by a variety of means, including via direct contact, aerosols, droplets, contaminated food or water, sexual contact, blood, tissue products, organ transplantation, or arthropod vectors, such as mosquitoes or ticks. Emerging infections, including most recently severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can spread quickly in the global era. If appropriately diagnosed, infections are often treatable, with many being curable. The diagnostic evaluation for infectious diseases requires knowledge of the appropriate test(s) to order, as well as their correct interpretation. Testing includes not only stains and cultures but also the detection of antibodies and antigens, as well as the increasing use of nucleic acid amplification tests, such as the polymerase chain reaction, and sequencing.