Chapter 22: Human Age and Microorganisms

Cytomegalovirus represents the most frequently transmitted pathogen during pregnancy, while congenital rubella and toxoplasmosis illustrate how maternal prevention strategies, such as avoiding raw meat and cat litter contact, can reduce vertical transmission. Newborns rely entirely on passive immunity through maternal IgG antibodies transported across the placenta and IgA/IgG delivered via colostrum and breast milk, making them vulnerable to infections like impetigo neonatorum and infant botulism, the latter flourishing because the immature gastrointestinal tract lacks established competitive microflora. As children develop through daycare and school environments, active immune maturation accelerates through repeated antigen exposure. Young adults generally maintain robust immune responses but experience distinct epidemiological patterns, including infectious mononucleosis and disproportionately high sexually transmitted infection rates, with adolescents and young adults representing nearly half of new STI cases nationally. New occupational and environmental exposures during this life stage require continuous antibody production and adaptive immune responses. In contrast, older adults undergo immune senescence, a progressive functional decline in immune competence that compromises both innate and adaptive immune mechanisms, resulting in prolonged infection recovery, increased disease severity, and heightened mortality risk from infectious agents. The elderly population faces particular diagnostic challenges because classic infection indicators such as fever and elevated white blood cell counts may be absent or present atypically. Influenza, urinary tract infections, and community-acquired pneumonia emerge as leading causes of morbidity and mortality in those over age sixty-five, with pneumonia frequently representing the terminal event in chronic illness. Age-related vulnerability is compounded by concurrent chronic diseases, polypharmacy effects, and increased healthcare facility residency, all of which synergistically elevate infection risk across this vulnerable population.