Table 1.
Identified causal pathogen in studies with head-to-head comparison between younger and elderly patients
| Pathogens | Young patientsa,c (%) | Elderly patientsb,c (%) | References |
|---|---|---|---|
| Streptococcus pneumoniae | 9–35 | 8.6–36 | [10–16] |
| Staphylococcus aureus | 0.3–4 | 0.0–5 | [11–13, 15, 16] |
| Haemophilus influenzae | 1–2 | 0.7–10 | [10–13, 15, 16] |
| Gram-negatives | 0–7 | 1.4–15 | [10–13, 15] |
| Enterobacteriaceae | 0.4–1.3 | 0.9–2.6 | [13, 16] |
| Atypical pathogens | 11–37 | 1–15 | [10, 11, 13–15] |
| Legionella pneumophila | 3.4–5.2 | 1–5 | [10–16] |
| Mycoplasma pneumoniae | 2.8–15 | 0–3.2 | [10–16] |
| Coxiella burnetti | 0.7–15.8 | 0–3.5 | [10, 13–15] |
| Chlamydia pneumoniae | 0.1–8.2 | 0–6.7 | [10, 12–16] |
| Total viral pathogens | 3.6–4 | 4.5–13.4 | [10, 11, 14, 15] |
| Influenza | 1.2–3.0 | 0.3–4.8 | [10, 12, 14–16] |
| Parainfluenza | 1.3 | 1–8.6 | [10, 14] |
| Respiratory syncytial virus | 0.0–0.4 | 0.7–1.8 | [10, 12, 15] |
| Unknown | 24–79 | 40–80 | [10–16] |
aLess than 65 years of age, except van Vught et al. [11] (< 50 years of age). The paper by Fernández Sabé et al. [10] has been excluded for this specific younger age group as their cut-off was 80 years of age; otherwise this younger age group also included patients aged 65–80 years
bLess than 65 years of age; however, exceptions are Fernández Sabé et al. [10] (> 80 years of age) and Van Vught et al. [11] (> 80 years of age)
cA range of reported prevalences of pathogens were found in the literature