The Certification Study Guide (6th edition) emphasizes that an outbreak should be suspected when there is an unexpected clustering of infections by time, place, and person, particularly when cases share a common exposure or procedure. Option D meets all key criteria for outbreak suspicion: the same organism (methicillin-resistant Staphylococcus aureus), the same location (cardiac ICU), a common procedure (cardiac surgery), and a tight time frame (same week). This constellation strongly suggests possible transmission related to surgical practices, postoperative care, or shared equipment.

The other scenarios reflect situations that do not necessarily indicate an outbreak. Routine environmental cultures are not recommended for outbreak detection and often do not correlate with patient infection risk. An apparent increase in ventilator-associated pneumonia following implementation of a new case definition is likely due to surveillance artifact, not true transmission. Similarly, increases in carbapenemase-producing Klebsiella pneumoniae after adoption of new laboratory breakpoints reflect diagnostic changes, not an epidemiologic event.

The study guide stresses the importance of distinguishing true outbreaks from pseudo-outbreaks caused by changes in definitions, testing methods, or surveillance intensity. CIC exam questions frequently test this concept. Recognizing a true outbreak requires linking cases through epidemiologic characteristics—not simply increases in numbers.

Prompt recognition of true outbreaks enables timely investigation, implementation of control measures, and prevention of further transmission.