Approach to the id patient

Here are the key points about the approach to patients with suspected infectious diseases:

1. History is critical and should focus on exposure history (previous infections, social history, diet, animal exposures, travel) and host-specific factors (immune status, immunizations). 

2. Physical exam should be thorough. Key components:

- Vital signs: Fever is common but not specific. Relative bradycardia can occur with some infections. 

- Lymphatics: Characterize adenopathy as localized vs generalized. 

- Skin: Do a complete exam, rashes can narrow the differential.

- Foreign bodies: Breaches in barriers from lines/drains/tubes are risk factors.

3. Diagnostic testing:

- WBC: Leukocytosis common with bacterial infections. Differential can suggest bacterial, viral, or parasitic. 

- ESR/CRP: Nonspecific inflammatory markers. Very high ESR (>100) has 90% predictive value for serious disease.

- CSF: Cell counts, glucose, protein, Gram stain, culture are key. PCR increasingly used for rapid diagnosis.  

- Cultures: Ideally get before antibiotics. Interpret in clinical context.

- Pathogen-specific tests: Serology, antigens, PCR can rapidly identify some organisms.

- Radiology: Evaluates deep sites, can guide sampling. Modality based on clinical question.

4. Treatment: Empiric antibiotics often needed before cultures, should be narrowed when possible. Consider adjuncts like IVIG in some cases.

5. Infection control: Isolation precautions are important to prevent transmission. CDC has published guidelines.

In summary, a detailed history, thorough exam, and thoughtful use of diagnostic testing allows clinicians to generate a focused differential and initiate appropriate empiric therapy while pursuing a definitive microbiologic diagnosis. Infection control is crucial to protect others.