Lower Respiratory Tract Infections: Pneumonia PDF

Lower Respiratory Tract Infections: Pneumonia Dr. Nihar Dash, MD Clinical Science Department College of Medicine 1 Key Learning Objectives 1. Define and classify pneumonia 2. List risk factors and etiology of pneumonia 3. Discuss the microbi...

Lower Respiratory Tract Infections: Pneumonia Dr. Nihar Dash, MD Clinical Science Department College of Medicine 1 Key Learning Objectives 1. Define and classify pneumonia 2. List risk factors and etiology of pneumonia 3. Discuss the microbiology of leading pathogens causing pneumonia 4. Clinical presentations of pneumonia 5. Interpret the laboratory diagnosis of pneumonia 2 Pneumonia  Pneumonia is an acute inflammatory process of the lung parenchyma caused by microbes  Pneumonia remains the leading cause of death from infection  one of the top 10 causes of death – no is 6 3 Classification of pneumonia  Clinical classification  community acquired vs hospital acquired  typical vs atypical pneumonia  Etiological classification  bacterial vs viral/ fungal  Morphological classification  lobar vs broncho vs interstitial pneumonia Clinical Classification of Pneumonia  because causative organisms are likely to be different and therefore treatment will likely differ  based on the setting where pneumonia develops, it can be classified as follows:  Community-acquired pneumonia (CAP) - Pneumonia occurring in any patient in the community  Healthcare-associated pneumonia (HCAP):  Hospital-acquired pneumonia (HAP) - Pneumonia developing ≥ 48 hours after admission to the hospital  Ventilator-associated pneumonia (VAP) - HAP that develops in patients who have been intubated and have received mechanical ventilation for at least 48 hours (MRSA/ESBL)  Pneumonia in an immunocmpromised patient 5 Morphological classification  Lobar Pneumonia – affecting single lobe (localized)  Bronchopneumonia – affecting patches throughout both lungs (diffuse)  Interstitial – involving areas in between the alveoli Risk factors  Age- Children under 2 years old and people 65 years old  Chronic diseases- asthma or HIV/AIDS affects  Smoking  Environmental factors – air pollution Common Clinical Presentations of Pneumonia  Fever  Cough with or without mucus  Shortness of breath  Chest pain that gets worse with deep breathing or cough  Low oxygen levels in your blood 7 Etiology of pneumonia  80% pneumonias in infants and children are caused by viruses  80% pneumonias in adults are bacterial  Etiology of CAP is strongly age dependent  Microaspiration of oropharyngeal secretions is the most common route by which these microbial agents reach the lung  Respiratory syncytial virus is the most common viral cause of pneumonia  Streptococcus pneumoniae is the most common cause of bacterial pneumonia in children.  Pneumocystis jiroveci is one of the most common causes of pneumoniainfected with HIV 8 Etiologic agents of pneumonia 2 months to 5 years of age RSV, Influenza, Parainfluenza, Adeno viruses – most common H. influenzae, S. pneumoniae, S. aureus – common bacterial agents 5- 14 years M. pneumniae, C.pneumoniae – leading bacterial causes Adults S. pneumoniae – most common C. pneumoniae, M. pneumoniae, Influenza viruses HAP/VAP P. aeruginosa, Enterobacter, Klebsiella, S. aureus (MRSA) and Legionella pneumophilla Chronic M. tuberculosis, Actinomyces ICP P. jiroveci, Nocardia, Legionella, MAC Viruses – causing pneumonia  RSV  Influenza  Coronavirus (COVID-19)  Parainfluenza  Adeno Respiratory Syncytial Virus RNA virus - Paramyxovirus family enveloped single-stranded, nonsegmented genome form syncytium – fuse cell lining RSV infections – droplet borne  MC cause of bronchitis ,broncholitis and Pneumonia in children less than 2 years of age  MC cause of fatal acute respiratory tract infection in infants and young children  MC hospital acquired viral infections  especially infect premature infants and children with congenital heart disease and chronic lung disease Laboratory diagnostic antigen detection – rapid tests for RSV infection RT-PCR include Palivizumab is a monoclonal antibody given to high-risk infants and young children as immunoprophylaxis 12 Influenza virus  commonly known as flu virus  belongs to Orthomyxoviridae family  enveloped  Segmented RNA genome  three influenza viruses A, B and C  A causes pandemics – circulates between man-animals  B causes outbreaks – man only  C rare and man only  causes acute respiratory tract infections  a contagious respiratory disease  genetic instability – drift (B) and shift (A) The genome is divided into eight segments that encode 11 viral proteins in total (HA, NA, M1, M2, NP, NS1, NS2, PA, PB1, PB2, and PB1-F2) 13 HA and NA  The viral envelope contains the transmembrane proteins HA and NA  HA – Hemagglutinin – attachment  NA – Neuraminidase – detachment  HA subtypes – H1 to H16 and NA subtypes – N1 TO N11  Subtypes are defined by the combination of the antigenic H and N proteins in the viral envelope  most prevalent influenza A strains in humans in the last 30 years have been H1N1and H3N2 14 Shift and Drift  The segmented genome facilitates the development of new strains through the mutation and reassortment  Reassortment – sudden – major change - shift - pandemics  Mutation – slow – minor change - drift – epidemics  Influenza A – can infect – man, pig and birds – prone to reassortment  Influenza A and B – mutation – minor - drift – epidemics 15 Presentation and Prevention  vaccine preventable  annual vaccination  6months and above  inactivated influenza vaccine  trivalent or quadrivalent  one dose – administered intramuscularly 16 Bacteria causing pneumonia Streptococcus pneumoniae Mycoplasma pneumoniae Chlamydophilla pneumoniae Legionella pneumophilla Klebseilla pneumoniae Streptococcus pneumoniae  Gram positive diplococci  Catalse negative  Alpha hemolytic  Optochin sensitive  Bile soluble  Encapsulated – polysaccharide – major virulence factor – prevent phagocytosis – neurovirulence  More than 100 serotypes  Pneumococci are common inhabitants of the nasopharynx of 5–90% of healthy persons 18 Pneumococcal Pneumonia  Most infections are caused by endogenous spread from the colonized nasopharynx or oropharynx to distal site  After aspiration, bacteria multiply in the alveolar spaces  Generally localized to the lower lobes of the lungs – lobar pneumonia  Can present as generalized bronchopneumonia  Sudden onset  Fever with chills  Productive cough with blood-tinged sputum  Chest pain  Children (65 yrs) are at greatest risk for pneumococcal diseases  People with hematologic disorder (e.g., malignancy, sickle cell disease) or functional asplenia are at risk for fulminant sepsis 19 Laboratory Diagnosis  Clinical specimens  Sputum – staining and culture  Blood - culture  Urine – antigen detection  Gram stain – sensitive – Gram positive diplococci and pus cells  Culture – Sheep Blood Agar – alpha hemolytic colonies  AST - usually sensitive to most cell wall acting antibiotics Isolates identified by catalase (negative), susceptibility to optochin, and solubility in bile 20 Treatment and Prevention  Penicillin is the drug of choice - Penicillin G-resistant pneumococci have been reported  Erythromycin and newer macrolides (clarithromycin) are good alternatives  Vaccines: TWO multivalent vaccines consisting of 23 or 13 serotypes of S. pneumoniae capsules are available  Conjugate (PCV 13) and polysaccharide (PCV 23) vaccines  Recommended for people over 60 years of age, immunosuppressed, diabetic, sickle cell disease patients 21 Mycoplasma pneumoniae  smallest free-living bacteria  do not have a rigid cell wall  their cell membrane contains sterols  causes respiratory tract infections: tracheobronchitis and pneumonia  atypical pneumonia or walking pneumonia  spread via respiratory droplets during coughing episodes  P1 adhesin - binds to cilia on epithelial cells, - loss of ciliated epithelial cells  Primarily infects children between ages 5 and 15 years  Drug of choice is erythromycin, doxycycline, or newer fluoroquinolones 22 Chlamydophila pneumoniae  obligate intracellular bacteria  unique developmental cycle  metabolically inactive infectious forms (elementary bodies [EBs]  metabolically active, noninfectious forms (reticulate bodies [RBs]  causes sinusitis, pharyngitis, bronchitis, and pneumonia  infections cannot be differentiated from other atypical pneumonias  diagnosis of C. pneumoniae infections is difficult  Macrolides (erythromycin, azithromycin, and clarithromycin), doxycycline, or levofloxacin is recommended for treatment 23 Klebsiella pneumoniae  GNB in family enterobactericae  have a prominent capsule that is responsible for the mucoid appearance of isolated colonies and the enhanced virulence of the organisms in vivo  cause community- or hospital-acquired lobar pneumonia  Prone to multi drug resistance [ESBL] 24 Legionella pneumophilla  cause of both community-acquired and healthcare-associated – pneumonia  infection has been linked to water distribution systems with warm water systems typically implicated  Slender, pleomorphic gram-negative rods  Stains poorly with gram stain  Capable of replication in alveolar macrophages (and amoebae in nature)  Prevents phagolysosome fusion  Responsible for legionnaires disease (serious pneumonia)and Pontiac fever (mild flu like) 25 Pneumocystis carinii Pneumonia [PCP]  Pneumocystis jiroveci  fungus  opportunistic pathogen  most common causes of pneumonia in ICP (HIV)  present as bilateral interstitial pneumonia with pleural effusion  BAL is gold standard for diagnosis  Evidence of cyst like structure - Gomori Methenmine Sliver or Giemsa staining  PCR is highly sensitive  TMP-SMX preventive therapy if efficacious 26 Healthcare Associated Pneumonia HAP VAP 27 Ventilator-Associated Pneumonia  accounts for 20% of all nosocomial infections  reported crude mortality rate >70% VAP Prevention Bundle 28 References  Murray’s Medical Microbiology – 9th edt  emedicine.medscape.com  www.webmd.com  www.cdc.gov 29