The CBIC Certified Infection Control Exam Study Guide (6th edition) clearly distinguishes colonization from infection, a foundational concept in infection prevention and healthcare epidemiology. Colonization is defined as the presence and multiplication of microorganisms on or within a host without tissue invasion, damage, or clinical signs of disease. Individuals who are colonized do not exhibit symptoms and typically do not mount an inflammatory response.

Option C accurately reflects this definition and is the correct answer. Colonized organisms may be part of normal flora or may be potentially pathogenic organisms such as Staphylococcus aureus or multidrug-resistant organisms. Although colonization does not cause illness, colonized individuals can serve as reservoirs for transmission and may later develop infection if host defenses are compromised.

Option A is incorrect because tissue invasion, even without visible damage, represents infection rather than colonization. Option B describes infection caused by normal flora with an inflammatory response. Option D includes cellular change, which indicates tissue response and therefore infection.

For the CIC® exam, it is essential to understand that colonization involves microbial presence without host response, while infection requires tissue invasion and a corresponding inflammatory or immune reaction. This distinction is critical for surveillance definitions, isolation decisions, antimicrobial stewardship, and patient education.