PATHOLOGICAL :- Infection of alveoli, distal airways and interstitium of the lung that is manifested by increased weight of the lungs, replacement of the normal lung’s sponginess by consolidation and alveoli filled with WBC, RBC and fibrin.
CLINICAL :- Pneumonia is a constellation of symptoms and signs in combination with at least one opacity on chest radiography.
Detection of IgM antibody or demonstration of a 4-fold rise in titer of antibody to a particular agent between acute- and convalescent-phase serum samples generally is considered good evidence that this agent is the cause of CAP.
Amplification of the DNA or RNA of microorganisms that are not part of the pharyngeal flora (from microbial cells collected by throat swab) has been used to infer that the implicated microorganism is the cause of pneumonia.
Guidelines recommend empirical treatment based on:
Clinical trials showing efficacy of agents
Risk factors for antimicrobial resistance (e.g., age > 65 years, β-lactam therapy within the past 3 months, alcoholism, immunosuppressive illness, multiple medical comorbidities, exposure to a child in a day-care center)
Patients with risk factors for P. aeruginosa (e.g., bronchiectasis, malnutrition, treatment with > 10 mg of prednisone qd, HIV infection, broad-spectrum antibiotic therapy for > 7 days in the past month, prior P. aeruginosa infection)
Carbapenem or antipseudomonal cephalosporin or piperacillin/tazobactam (doses below) plus