Respiratory Infections: A Comprehensive Overview
Respiratory infections are a common health problem affecting people of all ages. They are caused by various microorganisms, including bacteria, viruses, and fungi. These infections can range from mild to severe, and can affect the upper respiratory tract (nose, throat, and sinuses) or the lower respiratory tract (lungs).
Common Respiratory Infections
1. Viral Infections:
➭ Respiratory Syncytial Virus (RSV): Primarily affects infants and young children, causing cold-like symptoms that can progress to pneumonia or bronchiolitis.
➭ Influenza: A highly contagious virus that can cause mild to severe illness. Symptoms include fever, cough, sore throat, muscle aches, and fatigue.
➭ COVID-19: A novel coronavirus that causes a range of symptoms, from mild to severe. In severe cases, it can lead to pneumonia and respiratory failure.
➭ Common Cold: Caused by various viruses, it typically results in mild symptoms like runny nose, sneezing, and sore throat.
2. Bacterial Infections:
➭ Streptococcal Pharyngitis (Strep Throat): A bacterial infection that causes sore throat, fever, and swollen lymph nodes.
➭ Pneumonia: An infection that inflames the air sacs in the lungs. It can be caused by bacteria, viruses, or fungi. Symptoms include cough, fever, chills, and difficulty breathing.
➭ Tuberculosis: A chronic bacterial infection that primarily affects the lungs. It can spread through the air and cause symptoms like cough, fever, night sweats, and weight loss.
3. Fungal Infections:
➭ Histoplasmosis: A fungal infection caused by inhaling spores of the Histoplasma capsulatum fungus. It can cause flu-like symptoms or a more severe lung infection.
➭ Blastomycosis: A fungal infection caused by inhaling spores of the Blastomyces dermatitidis fungus. It can cause flu-like symptoms, skin lesions, and respiratory problems.
➭ Coccidioidomycosis (Valley Fever): A fungal infection caused by inhaling spores of the Coccidioides immitis fungus. It can cause flu-like symptoms, pneumonia, and skin lesions.
Risk Factors for Respiratory Infections:
➭ Age: Infants, young children, and older adults are more susceptible to respiratory infections.
➭ Weakened Immune System: People with weakened immune systems, such as those with HIV/AIDS, cancer, or undergoing chemotherapy, are at increased risk.
➭ Exposure to Sick Individuals: Close contact with people who are infected can increase the risk of transmission.
➭ Smoking: Smoking damages the lungs and weakens the immune system, making individuals more vulnerable to respiratory infections.
➭ Environmental Factors: Exposure to air pollution, allergens, and other environmental factors can irritate the respiratory tract and increase the risk of infection.
Prevention and Treatment:
➭ Vaccination: Getting vaccinated against influenza and COVID-19 is essential for preventing these infections.
➭ Hand Hygiene: Frequent handwashing with soap and water is crucial to prevent the spread of germs.
➭ Healthy Lifestyle: Eating a balanced diet, getting enough sleep, and exercising regularly can boost the immune system.
➭ Avoid Exposure to Sick Individuals: Stay away from people who are ill to reduce the risk of infection.
➭ Treatment: Treatment for respiratory infections depends on the specific cause and severity of the illness. Antibiotics are used to treat bacterial infections, while antiviral medications may be used for viral infections. Fungal infections are treated with antifungal medications.
Pneumonia: A Lungs' Worst Nightmare
What is Pneumonia?
Pneumonia is an inflammation of the lungs caused by infection. The infection causes the air sacs in your lungs, called alveoli, to fill with fluid or pus. This makes it difficult for oxygen to reach your bloodstream.
Types of Pneumonia
There are two main types of pneumonia:
1. Community-Acquired Pneumonia (CAP): This type of pneumonia is acquired outside of a healthcare facility. It's the 8th leading cause of death, with a 12% mortality rate for hospitalized patients.
2. Hospital-Acquired Pneumonia (HAP): This type of pneumonia develops in a hospital setting, usually more than 48 hours after admission. It's the 2nd leading cause of nosocomial infections.
Pathophysiology
Pneumonia occurs when the body's lung defenses fail to prevent pathogen invasion. These defenses include:
➭ Mechanical filtering: Mucociliary clearance (cough)
➭ Antimicrobial substances: Cellular immunity
➭ Other factors: Age, immunosuppression, smoking, alcohol use, malignancies, COPD, endotracheal tubes, and certain medications.
Clinical Presentation
Pneumonia can present in two ways:
1. Typical Pneumonia:
➭ Onset: Rapid
➭ Appearance: Ill-appearing
➭ Symptoms: High fever, chills, chest pain, purulent sputum
➭ On exam: Crackles, consolidation, leukocytosis
➭ CXR: Airspace filling (lobar infiltrate)
➭ Pathogens: Streptococcus pneumoniae, Staphylococcus aureus, Gram-negative bacilli
2. Atypical Pneumonia:
➭ Onset: Indolent
➭ Appearance: Less ill, not decompensating
➭ Symptoms: Low-grade fever, malaise, headache, dry cough
➭ On exam: Crackles, no consolidation, mild or no leukocytosis
➭ CXR: Patchy interstitial infiltrates
➭ Pathogens: Mycoplasma, Chlamydia, Legionella, viruses
Diagnosis
➭ Imaging:
➭ Lobar: Entire lobe consolidation with air bronchograms
➭ Interstitial: Increased interstitial opacities
➭ Sputum gram stain and culture
➭ Blood cultures: For hospitalized patients
Prognosis
The CURB-65 score is used to assess the severity of pneumonia:
➭ 0-1: 1.5% mortality, outpatient care
➭ 2: 9.2% mortality, inpatient or observation
➭ >3: 22% mortality, inpatient (ICU if respiratory failure)
Treatment
➭ Outpatient:
⦿ Healthy: Amoxicillin or doxycycline
⦿ Comorbidities: Respiratory fluoroquinolone (levofloxacin) OR amoxicillin-clavulanate or cephalosporin AND macrolide or doxycycline
➭ Inpatient:
⦿ No MRSA risk: Beta-lactam + macrolide OR respiratory fluoroquinolone OR beta-lactam + doxycycline
⦿ MRSA or Pseudomonas risk: Vancomycin (MRSA), cefepime or piperacillin-tazobactam (Pseudomonas)
⦿ Aspiration suspected: Anaerobic coverage if lung abscess or empyema
Hospital-Acquired Pneumonia (HAP) and Ventilator-Associated Pneumonia (VAP)
HAP and VAP are serious infections that can occur in hospitalized patients, particularly those who are critically ill or on ventilators.
Risk Factors:
⦿ Underlying illnesses
⦿ Use of catheters
⦿ Endotracheal intubation
⦿ Severity of illness
⦿ Contaminated respiratory devices
⦿ Poor hygiene
Pathophysiology:
➭ Colonization: Pathogenic bacteria colonize the pharynx.
➭ Aspiration: Bacteria are aspirated into the lower respiratory tract.
Clinical Presentation:
⦿ Fever
⦿ Leukocytosis
⦿ New or worsening respiratory secretions
Diagnosis:
⦿ Clinical presentation
⦿ New or worsening infiltrates on chest X-ray or CT scan
Treatment:
Treatment for HAP/VAP is based on the local hospital flora and antibiotic susceptibility testing. Common pathogens include:
⦿Pseudomonas aeruginosa
⦿Enterobacter
⦿E. coli
⦿Klebsiella
⦿Acinetobacter
⦿MRSA
⦿ Anaerobes
Antibiotic choices:
➭ Pseudomonas Suspect: If gram-negative rods are seen on Gram stain or there is a history of prior antibiotic therapy or immunosuppression, consider:
➭ B-lactams: Piperacillin-tazobactam, cefepime, ceftazidime, or meropenem
➭ Non-B-lactam Fluoroquinolones: Ciprofloxacin or levofloxacin
➭ Aminoglycosides: Gentamicin
➭ Polymyxins: Colistin
➭ MRSA Suspect: If gram-positive cocci in clusters are seen on Gram stain or there is a history of recent influenza or IV drug use, consider:
➭ Glycopeptides: Vancomycin
➭ Oxazolidinones: Linezolid
Prevention:
⦿ Hand hygiene
⦿ Aseptic technique for invasive procedures
⦿ Early removal of invasive devices
⦿ Head-of-bed elevation for ventilated patients
Viral Infections
➭ RSV (Respiratory Syncytial Virus):
⦿ Nearly all children are infected by age 2-3.
⦿ It causes mucus and inflammatory material to occlude small airways, leading to lower respiratory tract infection.
⦿ Symptoms range from mild to severe.
➭ COVID-19:
⦿ Enveloped, single-stranded, non-segmented RNA virus.
⦿ Binds to the angiotensin-converting enzyme 2 (ACE2) receptor on host cells.
⦿ Increased risk of hospitalization and severe disease in patients with comorbidities.
⦿ Social health determinants play a role in disease severity.
➭ Influenza:
⦿ Significant health burden, can lead to pneumonia, croup, exacerbations, and increased severity in HIV patients.
⦿ Vaccination is the best way to prevent severe disease.
⦿ Neuraminidase inhibitors (Zanamivir, Oseltamivir, Peramivir) are used for treatment.
Mycobacterial Infections (Tuberculosis)
➭ Risk factors for exposure: Close contact with an infected person, immigration from areas with high incidence, young children, HIV patients, prior untreated TB, IV drug users, high-risk congregate settings, and TNF-alpha antagonist treatment.
➭ Pathophysiology:
⦿ M. tuberculosis is transmitted by aerosols and grows in macrophages.
⦿ TH1 response leads to macrophage activation and bacterial control.
➭ Clinical presentation:
⦿ Latent: Asymptomatic, but positive tuberculin skin test or IFN-gamma release assay.
⦿ Active: Weight loss, fever, night sweats, cough, hemoptysis.
➭ Diagnosis:
⦿ Latent: Tuberculin skin test or IFN-gamma release assay.
⦿ Active: Sputum AFB smear and culture.
➭ Treatment: Isoniazid, rifampin, ethambutol, pyrazinamide.
Additional points you could consider adding:
➭ Viral infections:
⦿ Discuss the importance of hygiene and vaccination in preventing viral infections.
⦿ Mention the role of antiviral medications in treating certain viral infections.
➭ Mycobacterial infections:
⦿ Highlight the importance of early diagnosis and treatment of tuberculosis to prevent its spread and progression to severe disease.
⦿ Discuss the challenges of treating multidrug-resistant tuberculosis.
Non-TB Mycobacterial Infections
➭ Epidemiology:
⦿ More common in HIV patients, immunocompromised individuals, and those with pulmonary disorders.
⦿ More prevalent in southern and midwestern US.
➭ Etiology:
⦿ Mycobacterium species are normal soil and water inhabitants.
⦿ Mycobacterium avium complex is the most common cause of pulmonary disease.
➭ Clinical Presentation:
⦿ Can lead to cavitary disease, bronchiectasis, and disseminated disease.
⦿ Mortality is uncommon.
➭ Treatment:
⦿ Difficult to treat.
⦿ Macrolide-sensitive: Azithromycin, rifampin, ethambutol, amikacin or streptomycin.
⦿ Macrolide-resistant: Clarithromycin, rifampin, ethambutol, amikacin or streptomycin.
Fungal Infections
➭ Epidemiology:
⦿ Immunocompromised individuals are at higher risk.
⦿ Others at risk in HIV patients: Cryptococcus, Histoplasma, Coccidioides, Kaposi sarcoma.
➭ Pathophysiology:
⦿ Disrupted defense mechanisms.
➭ Endemic Mycoses:
⦿ Histoplasma capsulatum: Midwest/Southeast US
⦿ Blastomyces dermatitidis: Southeast US
⦿ Coccidioides immitis: Valley fever (Arizona)
➭ Clinical Presentation:
⦿ Asymptomatic or mild/non-specific symptoms.
⦿ Can lead to severe disease with respiratory, skin, and disseminated manifestations.
➭ Diagnosis:
⦿ Tissue culture, skin test, serology.
➭ Treatment:
⦿ Varies depending on the specific fungal infection.
⦿ Common antifungal agents include: itraconazole, amphotericin B, fluconazole, voriconazole.
Additional points you could consider adding:
➭ Non-TB Mycobacterial Infections:
⦿ Discuss the importance of early diagnosis and treatment to prevent disease progression.
⦿ Highlight the challenges of treating multidrug-resistant mycobacterial infections.
➭ Fungal Infections:
⦿ Emphasize the importance of risk factor awareness and early diagnosis in preventing severe fungal infections.
⦿ Discuss the role of antifungal prophylaxis in high-risk individuals.
