Why must precautions often begin before the laboratory confirms a diagnosis?

1. Laboratory tests that depend on culture techniques often require two or more days for completion. 2. Every hour of that delay is an hour the agent can spread if no barrier is in place. 3. So precautions are applied empirically for syndromes that carry a sufficiently high risk while confirmatory tests are pending. 4. Reporting without delay is the opposite of the stated problem. 5. Empiric precautions do not replace testing, since the result is what later modifies or stops them. 6. Not every patient needing precautions can be identified in advance, which is why syndromes rather than diagnoses trigger the decision. _Source: CDC Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings (2007), Part III, section III.C. Syndromic and Empiric Applications of Transmission-Based Precautions_