Colonization vs Infection
Colonization is the presence, growth, and multiplication of the organism without observable clinical symptoms or immune reaction.
1. MRSA – Colonization may occur in: the nares; axillae; chronic wounds or decubitus ulcer surface; perineum; around gastrostomy and tracheostomy sites; in the sputum or urine; and on healthy skin. One of the most common sites of colonization in both patients and employees is the nose (anterior nares). While healthcare workers may become colonized with MRSA (as they may with susceptible S. aureus), they rarely develop infections.
2. Enterococci – Are normally found in the bowel, the female genital tract, and the mouth. Strains resistant to vancomycin (VRE) may survive and multiply, resulting in a colonization of the bowel.
3. C. difficile – Commonly found in the gastrointestinal tract, the organism including drug-resistant and “epidemic strains” can asymptomatically colonize the bowel of individuals. Patients receiving antimicrobial therapy may be especially susceptible to developing CDI. Generally, there are more asymptomatic carriers than CDI patients. Though no symptoms may be evident, the colonized patient may test positive for the organism or its toxin(s).
4. Multidrug-Resistant Gram-Negative Bacilli (MDR-GNB) – Colonization may occur on the skin (healthy skin and wounds) and the respiratory tract of both healthcare workers and patients. Colonization may also occur in the bowel where these organisms may occur as normal intestinal flora. As with other MDROs, infection of healthcare workers is rare.
a. A. baumannii – Colonization may occur on multiple areas of the skin including the axillae and groin, as well as the respiratory tract of both patients and healthy individuals. Patients may also be colonized in wounds and occasionally the bowel. Colonization is particularly heavy during outbreaks.
b. K. pneumoniae and other Enterobacteriaceae – May colonize wounds, healthy skin, the bowel, and the respiratory tract of patients and healthcare workers.
Infection refers to the invasion of bacteria into tissue with replication of the organism. Infection is characterized by isolation of the organism accompanied by clinical signs of illness such as fever, elevated white blood count, purulence (pus), and clinical expression of disease such as pneumonia, bloodstream infections, urinary tract infections, gastrointestinal infections, and skin infections.