Domain 1: Identification of Infectious Disease Processes
Identification of Infectious Disease Processes tests how well you connect microbiology and host response to infection prevention decisions: recognizing syndromes, interpreting laboratory results, and distinguishing colonization from infection.
Core rules and concepts
- The chain of infection requires a pathogen, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host; breaking any link can prevent transmission.
- Gram stain gives rapid morphology and inflammatory context; culture identifies the organism and allows susceptibility testing. MIC values are interpreted with CLSI or FDA breakpoints, not by guesswork.
- NAATs detect nucleic acid and can remain positive after organism death; serology detects antibody and may be negative early in infection (window period).
- Colonization means the organism is present without clinical signs of infection; it should not automatically be treated.
Worked example
A 68-year-old afebrile patient has one of four blood culture bottles positive for coagulase-negative staphylococci after 36 hours, with no central line or prosthetic material. Coagulase-negative staphylococci are common skin flora, and a single positive bottle often represents contamination. The reasoning is to assess bottle number, organism, and clinical findings before labeling bacteremia; repeat cultures if suspicion persists. Treating the isolate as true bacteremia would invite unnecessary vancomycin and potential resistance.
Traps
A positive NAAT does not prove active infection; a negative serology does not exclude early infection; a sputum culture may reflect oral colonization; and a positive urine culture without symptoms may be asymptomatic bacteriuria, not UTI.