Diseases of the Lower Respiratory Tract Classification Causative organisms Laboratory diagnosis 1. Introduction What counts as a lower respiratory infection Lower respiratory tract infections include tracheitis, bronchitis, bronchiolitis, pneumonitis, pneumonia and pleurisy. Pneumonitis Inflammation of the alveoli. Pneumonia The alveoli fill with pus and fluid. Pleurisy Inflammation of the pleura. Typical and atypical pneumonia Typical Fever, pleuritic chest pain and a productive cough with sputum. Atypical Sputum is scanty or absent. This classification is not much help in diagnosis, since sputum may be mucoid and profuse even with atypical pneumonia. Classification into community-acquired and nosocomial pneumonias is more helpful for the management of patients. Pneumonia Community-acquired Healthcare-associated Bacterial Viral Fungal Early onset Late onsetMedical Microbiology · Undergraduate TextTracheitis, bronchitis, bronchiolitis, pneumonitis, pneumonia and pleurisy, with a focus on how pneumonia is classified, what causes it, and how it is diagnosed.

2. Community-acquired pneumonia Causes grouped by type of organism Bacterial pneumonia Viral pneumonia Viral infections may set the stage for secondary bacterial infections. Fungal pneumonia Streptococcus pneumoniae most common H. influenzae M. catarrhalis Mycobacterium tuberculosis Mycoplasma pneumoniae in school-age students through young adulthood Coxiella burnetti Q fever Uncommon: K. pneumoniae, P. aeruginosa, Legionella, Chlamydophila pneumonia, Chlamydophila psittaci, S. aureus, S. agalactiae Influenza A virus Respiratory syncytial virus in infants and young children Pneumocystis jeroveci causes disease among immunocompromised patients, especially AIDS patients Dimorphic fungi: Histoplasma capsulatum, Blastomyces dermatitidis and Coccidioides immitis Filamentous fungi (moulds): Aspergillus, Rhizopus and Mucor

3. Healthcare-associated pneumonia Either early onset or late onset Early onset Late onset Hospital admission First 4 days of hospitalization → A) Early onset pneumonia Occurs during the first 4 days of hospitalization. It is rare and is often caused by: 1. Moraxella catarrhalis 2. H. influenzae 3. S. pneumoniae 4. Viruses (e.g. influenza A and B viruses or respiratory syncytial virus) B) Late onset pneumonia The commonest form. It is caused by: Enterobacteriaceae 40% S. aureus 25% P. aeruginosa 15% 1. Enterobacteriaceae (40%): K. pneumoniae, Serratia marcescens, etc. 2. Staphylococcus aureus (25%) including methicillin-resistant S. aureus 3. Gram-negative bacilli: P. aeruginosa (15%) and Acinetobacter species 4. Filamentous fungi (moulds): Aspergillus 5. Yeasts such as Cryptococcus neoformans

4. Laboratory diagnosis From specimen to aetiology ≥ 25 WBCs per low power field ≤ 10 squamous epithelial cells per low power field Blood culture 30% Positive blood cultures are very helpful in diagnosis because 30% of cases of bacterial pneumonia have bacteraemia. 1 Collect specimens Sputum and blood specimens must be collected. Sometimes a lung biopsy is required. Deep cough Induction Aspiration Bronchoalveolar lavage (BAL) 2 Gram stain the smear Smears must be examined first to determine that it is a true sputum and not saliva. 3 Check that it is purulent sputum Secretions from the lungs, bronchi, or trachea that contain: 4 Apply diagnostic methods Acceptable specimens are then subjected to the different methods of diagnosis to determine the aetiology of pneumonia.