Microbial aetiology: based on detailed tests performed October 4, 1998–October 3, 1999. Cases include those with nursing home acquired pneumonia (NHAP). Controls are age- and sex-matched patients with community acquired pneumonia (CAP), not NHAP
| Cases | Controls | |
| Subjects n | 22 | 44 |
| Pathogen detected | 15 (68) | 35 (80) |
| Bacterial | 13 (59) | 24 (55) |
| Atypical | 4 (18) | 9 (20) |
| Viral | 3 (14) | 15 (34) |
| Mixed | 5 (23) | 14 (32) |
| Streptococcus pneumoniae | 12 (55) | 19 (43) |
| Staphylococcus aureus | 0 | 1 |
| Moraxella catarrhalis | 1 | 1 |
| Haemophilus influenzae | 0 | 5 (11) |
| Chlamydia pneumoniae | 4 (18) | 7 (16) |
| Chlamydia psittaci | 0 | 1 |
| Legionella sp. | 0 | 1 |
| Influenza A virus | 0 | 14 (32) |
| Influenza B virus | 0 | 1 |
| Respiratory syncytial virus | 3 (14) | 0 |
Data are presented as n (%) unless otherwise stated