What can cause infections or inflammatory conditions?

Causes of Infections and Inflammatory Conditions

Infections and inflammatory conditions can be caused by pathogens (viruses, bacteria, fungi, parasites), autoimmune processes, physical or chemical injuries, and systemic inflammatory disorders. Understanding these causes is essential for proper diagnosis and treatment.

Infectious Causes

Bacterial Infections

• Bacterial pathogens commonly cause infections in various body systems, including respiratory tract (Streptococcus pneumoniae, Haemophilus influenzae), skin (Staphylococcus aureus), and urinary tract (Escherichia coli) 1, 2
• Bacterial sinusitis typically follows viral upper respiratory infections in 0.5% to 13% of cases 1
• Bacterial keratitis (corneal infection) is often associated with contact lens wear, trauma, or compromised ocular surface 1

Viral Infections

• Viruses are common causes of respiratory infections, including sinusitis - with 40-90% of viral upper respiratory infections showing CT evidence of sinus involvement 1
• Acute viral infections often precede bacterial superinfections 1
• Viral agents like HSV, VZV, and Epstein-Barr can produce immunologically mediated corneal infiltrates that may resemble bacterial or fungal keratitis 1
• Viral infections are the most common cause of acute pericarditis and myocarditis 3

Fungal Infections

• Fungal pathogens (yeast and mold) can cause serious infections, particularly in immunocompromised hosts 1
• Invasive fungal sinusitis caused by phycomycetes (Absidia, Mucor, Rhizopus) or Aspergillus species can be rapidly progressive and potentially fatal in immunocompromised patients 1

Parasitic Infections

• Parasites including protozoa (such as Acanthamoeba) can cause keratitis, especially in contact lens wearers 1
• Nematodes like Onchocerca can cause infiltrative keratitis 1

Inflammatory Conditions

Autoimmune/Immune-Mediated Inflammation

• Systemic autoimmune diseases like rheumatoid arthritis, systemic lupus erythematosus, and vasculitic disorders can cause inflammatory conditions in multiple organs 1, 4
• Multisystem Inflammatory Syndrome in Children (MIS-C) is associated with SARS-CoV-2 infection and characterized by fever, mucocutaneous findings, cardiac dysfunction, and gastrointestinal symptoms 1
• Granulomatous inflammatory diseases like sarcoidosis can affect bones, joints, and other tissues 4

Inflammatory Cardiac Conditions

• Myocarditis is commonly caused by viruses but can also result from autoimmune processes 1, 3
• Acute pericarditis is typically viral in origin, presenting with characteristic chest pain and ECG changes 3
• Infective endocarditis involves infection of cardiac valves, chambers, or intracardiac devices, most commonly caused by Staphylococcus aureus 3

Bone and Joint Inflammation

• Osteomyelitis (bone infection) and septic arthritis (joint infection) can be caused by bacterial, fungal, or mycobacterial organisms 4
• Chronic bronchitis results from prolonged exposure to pulmonary irritants, most prominently cigarette smoke, with recurrent episodes of infection 1

Predisposing Factors

Immunocompromised States

• Primary immunodeficiency disorders (PIDDs) predispose patients to recurrent, severe, or unusual infections 1
• Secondary immunodeficiency from conditions like HIV/AIDS, malnutrition, or immunosuppressive therapy increases infection risk 1

Local Tissue Factors

• Contact lens wear, particularly extended wear, increases risk of bacterial keratitis 1
• Trauma, foreign bodies, and exposed sutures can lead to infectious or inflammatory keratitis 1
• Structural abnormalities can predispose to infections, such as in sinusitis 1

Systemic Conditions

• Diabetes mellitus and hematologic malignancies increase risk for invasive fungal infections 1
• Chronic conditions like cystic fibrosis predispose to recurrent respiratory infections 1

Pathophysiological Mechanisms

Inflammatory Response

• Inflammation is the body's protective response to pathogens or tissue damage, characterized by five cardinal signs: rubor (redness), calor (warmth), tumor (swelling), dolor (pain), and functio laesa (loss of function) 5, 6
• The inflammatory process involves vasodilation, increased vascular permeability, and leukocyte recruitment 5, 6

Leukocytosis

• Increased white blood cell count (leukocytosis) is a common laboratory finding in infections and inflammatory processes 7
• Physical stress, emotional stress, and medications (corticosteroids, lithium, beta agonists) can also cause leukocytosis 7
• Extremely elevated white blood cell counts or concurrent abnormalities in red blood cell or platelet counts may indicate primary bone marrow disorders 7

Diagnostic Considerations

• Imaging studies (radiography, CT, MRI) are important for diagnosing inflammatory and infectious conditions of the spine, sinuses, and other anatomical locations 1
• Laboratory markers including C-reactive protein, erythrocyte sedimentation rate, and procalcitonin can help identify and monitor inflammatory conditions 1
• Culture and susceptibility testing are essential for identifying specific infectious agents and guiding antimicrobial therapy 2
• Differential diagnosis should include both infectious and non-infectious causes of inflammation 1

Prevention Strategies

• Avoiding predisposing factors may reduce infection risk, such as proper contact lens care for preventing bacterial keratitis 1
• Patient education about risk factors and preventive measures is important 1
• Prophylactic antibiotics may be considered in high-risk situations, though this must be balanced against risks of bacterial resistance and drug toxicity 1