Diagnostic criteria for pneumonia used in the present study
| Criterion | Parameters | Evaluation/comments |
| Clinical | Body temperature >40°C | Admitted as positive when three of four (>50%) are present. The initial diagnosis of pneumonia is usually based on clinical features and all listed criteria are recognised as important constituents of this approach 13, 14 |
| Purulent mucus in the endotracheal tube | ||
| Difficulty breathing and tachypnoea | ||
| Cyanosis of the ears, lips and tongue | ||
| Radiological | Progressive infiltrate | Positive when at least one sign is present. Each of these signs alone is sensitive and indicative of pneumonia diagnosis in experiments 17 |
| Consolidation | ||
| Cavitations | ||
| Pleural effusion | ||
| Laboratory | Impairment of pulmonary function as defined by Pa,O2/FI,O2 ratio of <200 mmHg | Considered positive when at least two of three signs (>50%) are present. These signs of pneumonia are considered reliable and are widely used in clinical and experimental medicine 18 |
| White cell density >11000 or <4000 cells·μL−1 on ≥2 consecutive days | ||
| BALF cellular content ≥1.0×103 cells·mm−3 | ||
| Microbiological | S. pneumoniae burden of ≥1×104 cfu·g lung tissue-1 in at least one sample. | Considered positive when at least one of two signs is present. Microbiological evaluation of lung tissue and especially BALF represent the cornerstones of pneumonia diagnosis and are commonly used in both clinical and experimental medicine 18 |
| BALF S. pneumoniae concentration of ≥1×104 cfu·mL-1 | ||
| Macroscopic | Lung lesion scoring ≥3 (red congestion or higher#) in at least one lobe | Considered positive when at least one of two signs is present |
| Pleural exudate or fibrin deposits (or both) in at least one pleural cavity | ||
| Histological | Combination of accumulation of polymorphonuclear leukocytes in the capillaries and adjacent alveolar spaces in at least one sample | In many previous studies, post mortem morphological observations were considered the most dependable criteria for pneumonia 15, 18 |
Pa,O2: arterial oxygen tension; FI,O2: inspiratory oxygen fraction; BALF: bronchoalveolar lavage fluid; S. pneumoniae: Streptococcus pneumoniae; cfu: colony-forming unit. #: see table 2. 1 mmHg = 0.133 kPa.