Microbiological etiologies of CAP by age group
| Organism | 65–74 years | 75–84 years | ≥85 years | P value* |
| n | 3170 | 3269 | 2361 | |
| Staphylococcus aureus | 1000 (31.5) | 1087 (33.3) | 857 (36.3) | <0.001 |
| MSSA | 562 (17.7) | 572 (17.5) | 457 (19.4) | 0.16 |
| MRSA | 441 (13.9) | 518 (15.8) | 402 (17.0) | 0.005 |
| Escherichia coli | 340 (10.7) | 400 (12.2) | 381 (16.1) | <0.001 |
| Streptococcus pneumoniae | 750 (23.7) | 580 (17.7) | 407 (17.2) | <0.001 |
| Pseudomonas aeruginosa | 508 (16.0) | 505 (15.4) | 255 (10.8) | <0.001 |
| Klebsiella pneumoniae | 261 (8.2) | 278 (8.5) | 203 (8.6) | 0.87 |
| Proteus mirabilis | 83 (2.6) | 121 (3.7) | 81 (3.4) | 0.04 |
| Haemophilus influenzae | 136 (4.3) | 139 (4.3) | 107 (4.5) | 0.87 |
| Serratia marcescens | 54 (1.7) | 59 (1.8) | 19 (0.80) | 0.005 |
| Stenotrophomonas (Xanthomonas) maltophilia | 63 (2.0) | 52 (1.6) | 21 (0.89) | 0.005 |
| Klebsiella oxytoca | 37 (1.2) | 35 (1.1) | 33 (1.4) | 0.53 |
*Pearson’s χ2 tests.
CAP, community-acquired pneumonia; MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-sensitive Staphylococcus aureus.