Phases and Manifestations of Infection

Exam Tip: If a question asks about the "vague" stage of an illness where the patient feels "under the weather" but doesn't have a specific diagnosis yet, they are referring to the Prodromal phase.

Clinical Manifestations: Local vs. Systemic

As the infection progresses, the body responds both at the site of entry and throughout the entire system.

Local Manifestations

These are confined to the specific area where the pathogen entered or is multiplying. Common signs include:

• Pain and heat
• Redness (erythema)
• Swelling (edema)
• Loss of function
• Purulence (the presence of pus).

Systemic Manifestations

These are widespread effects that impact the entire body. Common signs include:

• Fever
• Weakness and malaise
• Headache
• Anorexia (loss of appetite)
• Nausea.

Complications: From Bacteremia to Septic Shock

In some cases, an infection can escalate into life-threatening complications.

• Bacteremia: The mere presence of bacteria in the blood.
• Septicemia: A more serious condition where bacteria in the blood trigger extensive inflammation and the release of vasoactive peptides and cytokines.
• Septic Shock: A critical complication where the release of these substances causes massive vasodilation (widening of blood vessels), leading to a dangerous drop in blood pressure.

Diagnostic Procedures and Laboratory Tests

To identify the specific microorganism and guide treatment, clinicians rely on several diagnostic tools.

Culture and Sensitivity

This is perhaps the most critical diagnostic step. A culture is performed to grow the organism from a sample (such as blood, urine, sputum, or a wound). Once the organism is grown, a sensitivity test is performed to determine which specific antibiotics will effectively kill that particular "bug".

Clinical Priority: Always collect the culture before administering the first dose of antibiotics. If antibiotics are given first, they may inhibit the growth of the bacteria in the lab, leading to a false-negative culture result.

Laboratory Values

• White Blood Cell (WBC) Count: An elevated WBC count (often found in a Complete Blood Count or CBC) typically indicates the body is fighting an infection.
• Erythrocyte Sedimentation Rate (ESR): An elevated ESR is a non-specific marker used to detect inflammation in the body.

Clinical Models: UTI and Hepatitis

Urinary Tract Infection (UTI)

A common infection occurs when bacteria, most frequently E. coli (which normally lives in the stool), move from the rectum into the urethra and ascend into the bladder.

• Manifestations: Dysuria (painful urination), urgency, frequency, hematuria (blood in urine), and cloudy/purulent urine.
• Diagnosis: History, physical exam, urinalysis, and urine culture.

Viral Hepatitis

Hepatitis involves inflammation of the liver caused by various viruses.

• Transmission: Hepatitis A and E are typically transmitted via the fecal-oral route (contaminated food/water), while Hepatitis B, C, and D are transmitted through contact with infected blood and body fluids.
• Manifestations: Jaundice (yellowing of the eyes/skin), clay-colored stools, and varying levels of hepatic necrosis.

Antimicrobial Stewardship

With the rise of antibiotic resistance—often caused by the overuse or incorrect use of antibiotics—healthcare providers must practice antimicrobial stewardship. The goal is simple but vital: "Right Bug, Right Drug". This means using targeted therapy based on culture and sensitivity results rather than relying solely on broad-spectrum antibiotics for extended periods.