Bacterial Infections and Mycobacterial Disease
Core concepts
Bacterial disease in children is mostly a question of age, anatomy, and host defense. Neonates: group B Streptococcus, Escherichia coli, Listeria monocytogenes. Toddlers: Streptococcus pneumoniae, Staphylococcus aureus, Kingella kingae. Adolescents: Neisseria meningitidis, S. aureus. Encapsulated organisms (H. influenzae type b, pneumococcus, meningococcus) explain asplenic risk. For mycobacteria, distinguish latent tuberculosis infection from active disease, and recognize nontuberculous mycobacteria (M. avium complex) as a cause of chronic unilateral cervical lymphadenitis in ages 1-5 years.
Traps
- Colonization is not infection: S. aureus and pneumococcus grow from respiratory secretions without disease.
- A negative tuberculin skin test or IGRA does not exclude active tuberculosis; IGRA is preferred at age 2 years and older and in BCG-vaccinated children.
- In suspected nontuberculous mycobacterial lymphadenitis, incision and drainage can create a fistula; excisional biopsy is preferred for diagnosis.
- Lyme disease is a clinical diagnosis when erythema migrans is present; serology can be falsely negative early.
Worked example
A 3-year-old has a 3-week enlarging, nontender, violaceous submandibular node, no fever, and normal examination. Think nontuberculous mycobacteria: obtain excisional biopsy for culture and histology rather than starting anti-staphylococcal antibiotics. By contrast, a 3-day warm, tender 2-cm node with fever suggests S. aureus or group A Streptococcus; if fluctuant, aspirate and drain.
Rule of thumb: match empiric coverage to the age-specific pathogen list and exact site, then de-escalate when culture and PCR results return.