What are the diagnostic criteria for common infections?

Diagnostic Criteria for Common Infections

The diagnosis of common infections requires specific clinical and laboratory criteria that vary by infection type, with standardized case definitions established by the Centers for Disease Control and Prevention (CDC) serving as the gold standard for accurate diagnosis. 1

Pelvic Inflammatory Disease (PID)

Required Clinical Criteria (all must be present):

• Lower abdominal tenderness
• Tenderness with motion of the cervix
• Adnexal tenderness

Plus at least ONE of the following:

• Positive test for C. trachomatis or gonorrhea
• Temperature >100.4°F (>38.0°C)
• Leukocytosis >10,000 WBC/mm³
• Purulent material in peritoneal cavity (via culdocentesis/laparoscopy)
• Pelvic abscess or inflammatory complex (on exam or imaging)
• Sexual contact with person known to have gonorrhea, chlamydia, or NGU 1

Rheumatic Fever

Major Criteria:

• Carditis
• Polyarthritis
• Chorea
• Subcutaneous nodules
• Erythema marginatum

Minor Criteria:

• Previous rheumatic fever/heart disease
• Arthralgia
• Fever
• Elevated ESR (≥60 mm/h in low-risk or ≥30 mm/h in high-risk populations), positive CRP (≥3.0 mg/dL), or leukocytosis
• Prolonged PR interval on ECG 1, 2

Diagnosis requires:

• Two major criteria OR one major plus two minor criteria
• PLUS evidence of preceding group A streptococcal infection (elevated ASO or other streptococcal antibodies, positive throat culture, or recent scarlet fever) 1, 2

Tularemia

Clinical Forms:

• Ulceroglandular: cutaneous ulcer with regional lymphadenopathy
• Glandular: regional lymphadenopathy without ulcer
• Oculoglandular: conjunctivitis with preauricular lymphadenopathy
• Oropharyngeal: stomatitis/pharyngitis/tonsillitis with cervical lymphadenopathy
• Intestinal: intestinal pain, vomiting, diarrhea
• Pneumonic: primary pleuropulmonary disease
• Typhoidal: febrile illness without early localizing signs 1

Laboratory Criteria:

• Presumptive: Elevated serum antibody titer to F. tularensis OR detection by fluorescent assay
• Confirmatory: Isolation of F. tularensis OR fourfold or greater change in antibody titer 1

Varicella (Chickenpox)

Clinical Definition:

• Acute onset of diffuse papulovesicular rash without other apparent cause

Laboratory Criteria:

• Isolation of varicella virus OR
• Significant rise in serum varicella IgG antibody 1

Skin and Soft Tissue Infections (SSTIs)

Impetigo:

• Discrete purulent lesions
• Causative agents: β-hemolytic streptococci and/or S. aureus
• Most common in children aged 2-5 years 1

Diabetic Foot Infections:

IDSA Classification:

1. Uninfected: No symptoms/signs of infection
2. Mild: Local infection (skin/subcutaneous tissue only), erythema 0.5-2 cm
3. Moderate: Local infection with erythema >2 cm OR deeper structures involved
4. Severe: Local infection with systemic inflammatory response syndrome (SIRS) signs:
   • Temperature >38°C or <36°C
   • Heart rate >90 beats/min
   • Respiratory rate >20 breaths/min or PaCO2 <32 mm Hg
   • WBC >12,000 or <4,000 cells/μL or ≥10% immature forms 1

Spine Infection

Clinical Indicators:

• Back pain with fever
• Elevated inflammatory markers (ESR, CRP)
• Risk factors: IV drug use, immunosuppression, diabetes
• Neurological deficits if epidural involvement

Diagnostic Approach:

• Blood cultures (at least 2 sets)
• MRI (preferred imaging modality)
• CT-guided or surgical biopsy for microbiological diagnosis 1

Meningitis

Clinical Presentation:

• Fever, headache, neck stiffness, altered mental status

Laboratory Criteria:

• CSF analysis (cell count, protein, glucose)
• Gram stain (sensitivity 60-80% in untreated patients)
• CSF culture
• Blood cultures (2-4 sets recommended)
• Molecular testing for viral pathogens (especially enteroviruses) 1

Important Considerations

Special Populations:

• Immunocompromised patients: Require aggressive diagnostic approach with early biopsy of skin/soft tissue lesions for cytology, histology, and culture 1
• Elderly patients: May present atypically with blunted fever response and altered mental status rather than classic symptoms 3

Diagnostic Pitfalls:

1. Relying solely on clinical presentation without appropriate laboratory confirmation
2. Failing to obtain cultures before starting antibiotics
3. Not considering local antimicrobial resistance patterns
4. Overlooking non-infectious causes that mimic infection
5. Missing deep-seated infections that present with subtle surface manifestations 1

Critical Diagnostic Steps:

1. Collect appropriate specimens before antimicrobial therapy when possible
2. Utilize both clinical criteria and laboratory confirmation
3. Consider epidemiological factors (travel, exposures, local pathogens)
4. Recognize that imaging may be necessary to determine extent of infection
5. Follow standardized case definitions for surveillance and reporting purposes 1