Primary prevention focuses on preventing the initial occurrence of disease or injury before it manifests, distinguishing it from secondary (early detection) and tertiary (mitigation of complications) prevention. The Certification Board of Infection Control and Epidemiology (CBIC) emphasizes the "Prevention and Control of Infectious Diseases" domain, which includes collaboration with public health agencies to implement preventive strategies, aligning with the Centers for Disease Control and Prevention (CDC) framework for infection prevention. The question requires identifying the activity that best fits primary prevention efforts.

Option C, "Promoting vaccination of health care workers and patients," is the correct answer. Vaccination is a cornerstone of primary prevention, as it prevents the onset of vaccine-preventable diseases (e.g., influenza, hepatitis B, measles) by inducing immunity before exposure. The CDC’s "Immunization of Health-Care Personnel" (2011) and "General Recommendations on Immunization" (2021) highlight the role of vaccination in protecting both healthcare workers and patients, reducing community transmission and healthcare-associated infections. Collaboration with public health agencies, which often oversee vaccination campaigns and supply distribution, enhances this effort, making it a proactive primary prevention strategy.

Option A, "Conducting outbreak investigations," is a secondary prevention activity. Outbreak investigations occur after cases are identified to control spread and mitigate impact, focusing on containment rather than preventing initial disease occurrence. The CDC’s "Principles of Epidemiology in Public Health Practice" (3rd Edition, 2012) classifies this as a response to an existing problem. Option B, "Performing surveillance for tuberculosis through tuberculin skin test," is also secondary prevention. Surveillance, including tuberculin skin testing, aims to detect latent or active tuberculosis early to prevent progression or transmission, not to prevent initial infection. The CDC’s "Guidelines for Preventing the Transmission of Mycobacterium tuberculosis" (2005) supports this as a screening tool. Option D, "Offering blood and body fluid post-exposure prophylaxis," is tertiary prevention. Post-exposure prophylaxis (e.g., for HIV or hepatitis B) is administered after potential exposure to prevent disease development, focusing on mitigating consequences rather than preventing initial exposure, as outlined in the CDC’s "Updated U.S. Public Health Service Guidelines" (2013).

The CBIC Practice Analysis (2022) and CDC guidelines prioritize vaccination as a primary prevention strategy, and collaboration with public health agencies amplifies its reach. Option C best reflects this preventive focus, making it the correct choice.