Determining the Cause

Chief Complaint: Recurrent Infections

The goal is to identify whether the infections are due to a local problem, an underlying systemic disease, or an immune system disorder.

A. History: Skin Infection

B. Culture and Sensitivity: MethicillinResistant Staphylococcus Aureus

MRSA cultured in Blood Agar. Bacterial ...

MRSA on blood agar. Methicillin resistant Staphylococcus aureus.

Reference images illustrating the typical appearance of MRSA (Methicillin-Resistant Staphylococcus aureus) on various culture media:

1. Blood Agar

  • Appearance: MRSA colonies on blood agar are round, smooth, and convex.

  • Color: They often appear golden-yellow to white.

  • Hemolysis: Typically exhibit beta-hemolysis, characterized by clear zones surrounding the colonies due to complete lysis of red blood cells.

MRSA on Blood Agar

Image Source: ResearchGate

2. Mannitol Salt Agar (MSA)

  • Selective and Differential Medium: High salt concentration inhibits most bacteria except staphylococci; mannitol fermentation differentiates species.

  • MRSA Characteristics:

    • Growth: MRSA grows well due to salt tolerance.

    • Mannitol Fermentation: Ferments mannitol, producing acid that turns the medium yellow around the colonies.(Getty Images)

MRSA on Mannitol Salt Agar

Image Source: Microbe Online

3. CHROMagar MRSA

  • Chromogenic Medium: Designed for selective identification of MRSA.

  • MRSA Appearance: Colonies appear pink to mauve after incubation.

  • Other Bacteria: Non-MRSA organisms are usually inhibited or appear colorless.(Chromagar)

MRSA on CHROMagar

Image Source: CHROMagar

These images should provide a clear visual reference for identifying MRSA on different culture media. If you need further information or additional images, feel free to ask!

 

  • Rule out MRSA, fungal, or atypical mycobacteria

  • If fungal, do KOH prep or fungal culture

  • Consider PCR for certain pathogens (e.g., herpes simplex)

 

 

Next Pivotal Assessment Findings
     

Determining the cause of recurrent skin infections involves a systematic approach. These infections can be due to various underlying factors, and identifying the root cause is crucial for effective management and prevention.

1. Detailed Medical History

Ask about:

  • Frequency and location of infections

  • Type of infection (boils, abscesses, cellulitis, fungal, etc.)

  • Hygiene practices

  • Close contacts with similar infections

  • Underlying chronic diseases (especially diabetes, HIV, malignancy)

  • Skin conditions (eczema, psoriasis, acne)

  • Medications, including immunosuppressants or steroids

  • Occupational exposure or sports involvement (e.g., wrestling, healthcare)

2. Physical Examination

Look for:

  • Distribution pattern (localized vs. generalized)

  • Signs of chronic skin conditions

  • Signs of systemic illness (weight loss, lymphadenopathy)

  • Presence of foreign bodies or wounds

3. Microbiological Testing

Perform culture and sensitivity testing:

  • Swab purulent lesions, aspirate abscesses, or biopsy chronic lesions

  • Rule out MRSA, fungal, or atypical mycobacteria

  • If fungal, do KOH prep or fungal culture

  • Consider PCR for certain pathogens (e.g., herpes simplex)

4. Screen for Underlying Conditions

Check for predisposing systemic conditions:

a. Metabolic

  • Diabetes mellitus (check fasting glucose or HbA1c)

b. Immunologic

  • CBC with differential (check for neutropenia or lymphopenia)

  • HIV test if indicated

  • Immunoglobulin levels (IgG, IgA, IgM) if suspect immunodeficiency

  • Consider neutrophil function tests for rare cases (e.g., chronic granulomatous disease in children)

c. Nutritional deficiencies

  • Zinc, iron, or protein deficiency can impair skin integrity and immunity

5. Dermatologic Evaluation

If recurrent infections occur over skin with dermatitis or other pathology, a dermatologist can help identify:

  • Contact dermatitis

  • Seborrheic dermatitis

  • Fungal superinfection

6. Environmental or Behavioral Factors

  • Crowded living conditions

  • Shared towels, razors

  • Poor wound care

  • Use of IV drugs or tattoos

  • Pets (for zoonotic fungal infections)

7. Recurrent Abscesses or Boils

If the infection is specifically recurrent furunculosis:

  • Consider chronic nasal carriage of Staph aureus – do nasal swabs

  • Family screening may be needed

  • Mupirocin nasal ointment and chlorhexidine body wash may help eradicate colonization

8. Genetic or Rare Disorders (if early-onset or severe)

  • Chronic granulomatous disease (CGD)

  • Hyper-IgE syndrome (Job's syndrome)

  • Severe Combined Immunodeficiency (SCID) – in infants

Summary Algorithm:

  1. Take a thorough history and exam

  2. Culture the lesion

  3. Check bloodwork for diabetes, CBC, HIV

  4. Assess immune status if recurrent/severe

  5. Evaluate skin conditions

  6. Investigate environmental and personal hygiene factors

Would you like a flowchart or checklist to guide evaluation in clinical practice?

 

 

Determining the cause of recurrent infections involves a systematic approach that includes clinical history, physical examination, laboratory testing, imaging, and sometimes referral to a specialist.

1. Detailed Clinical History

  • Type of infections: Skin, respiratory, urinary, gastrointestinal, etc.

  • Frequency and duration: How often and how long they last.

  • Severity: Mild or requiring hospitalization/IV antibiotics.

  • Location: Same site or multiple different sites.

  • Response to treatment: Partial, complete, or resistant to antibiotics.

  • Family history: Immune deficiencies or autoimmune diseases.

  • Environmental exposure: Travel, pets, work, daycare, etc.

  • Medications: Immunosuppressants, steroids, chemotherapy.

  • Vaccination history: Especially pneumococcus, influenza, etc.

2. Physical Examination

  • Look for signs of chronic illness, lymphadenopathy, organomegaly.

  • Examine affected areas (e.g., sinuses, lungs, skin, urinary tract).

3. Laboratory Tests

  • Complete blood count (CBC) with differential: Look for leukopenia or neutropenia.

  • Immunoglobulin levels (IgG, IgA, IgM, sometimes IgE).

  • Lymphocyte subsets (T cells, B cells, NK cells).

  • Complement levels (CH50, C3, C4).

  • Neutrophil function tests (e.g., nitroblue tetrazolium test or oxidative burst).

  • HIV testing (if risk factors or unexplained immunosuppression).

  • Diabetes screen: Elevated glucose can predispose to infections.

4. Microbiological Workup

  • Cultures of infected sites (blood, urine, sputum, wound, etc.).

  • Identify organisms: Recurrent infections with the same organism vs. different ones.

  • Look for antibiotic resistance patterns.

5. Imaging Studies

  • CT or MRI: Evaluate for chronic infection or anatomical defects (e.g., sinus CT, chest CT, abdominal imaging).

  • Ultrasound: For abscesses, urinary tract abnormalities.

6. Special Tests (If Indicated)

  • Sweat chloride test or genetic testing for cystic fibrosis.

  • Bronchoscopy: For recurrent pneumonia or unexplained cough.

  • Urinary tract imaging: For recurrent UTIs.

  • Bone marrow biopsy: If hematologic malignancy is suspected.

7. Referral to Specialist

  • Immunologist: For suspected primary or secondary immunodeficiencies.

  • Infectious disease specialist: For difficult-to-diagnose or manage infections.

  • Endocrinologist: For metabolic disorders like diabetes.

Common Categories of Causes

  • Anatomic defects (e.g., sinus blockage, vesicoureteral reflux)

  • Immunodeficiencies:

    • Primary (genetic, e.g., CVID, X-linked agammaglobulinemia)

    • Secondary (HIV, chemotherapy, immunosuppressants, diabetes)

  • Chronic diseases (e.g., diabetes, malignancy)

  • Environmental/behavioral factors (e.g., poor hygiene, overcrowding)

If you’d like, you can tell me more about the type of infections or symptoms you’re referring to, and I can help outline a more tailored diagnostic approach.

 

Differential Diagnosis


  • Immunodeficiency Disorders    :

    • Common Variable Immunodeficiency (CVID)
    • Selective IgA deficiency
    • IgG subclass deficiency
    • Severe Combined Immunodeficiency (SCID)
    • HIV/AIDS

  • Autoimmune Disorders:

    • Systemic Lupus Erythematosus (SLE)
    • Rheumatoid Arthritis (RA)
    • Sjögren's syndrome
    • Goodpasture syndrome

  • Chronic Medical Conditions:

    • Diabetes mellitus
    • Chronic kidney disease
    • Chronic liver disease
    • Chronic obstructive pulmonary disease (COPD)

  • Hematologic Disorders:

    • Leukemia
    • Lymphoma
    • Multiple Myeloma

  • Granulomatous Diseases:

    • Tuberculosis (TB)
    • Sarcoidosis
    • Crohn's disease
    • Wegener's granulomatosis

  • Allergic and Asthma Conditions:

    • Allergic rhinitis
    • Asthma

  • Underlying Anatomical Abnormalities:

    • Polyps in the sinuses
    • Bronchiectasis
    • Chronic sinusitis

  • Medications and Treatments:

    • Immunosuppressive medications
    • Chemotherapy

  • Environmental Exposures:

    • Occupational exposure to infectious agents
    • Mold exposure

  • Psychosocial Factors:

    • Chronic stress
    • Poor nutrition
    • Sleep deprivation

  • Underlying Viral Infections:

    • Chronic viral infections like hepatitis B or C

  • Underlying Bacterial Infections:

    • Chronic bacterial infections such as bronchiectasis or osteomyelitis

  • Underlying Fungal Infections:

    • Chronic fungal infections such as aspergillosis or candidiasis

  • Autoinflammatory Syndromes:

    • Familial Mediterranean Fever (FMF)
    • Periodic Fever Syndromes

  • Gastrointestinal Disorders:

    • Inflammatory Bowel Disease (IBD)

 

Next Pivotal Assessment

 

 

 

 

 

 

 

Infections, Recurrent

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