Baseline characteristics are presented in Tables 1, 2 and 3. One hundred and seven patients (42%) were female, and 72 were children (28%). Mean age in the group with viral infections was lower than in the remaining patients (29 vs. 47 years; p < 0.001) but the difference was not significant if children and adults were analyzed separately (children 4.3 vs. 5.7 years; p = 0.28; adults 53.6 vs. 56.6 years; p = 0.31). There were more patients with neutropenia, hematological malignancy or collagen vascular disease/vasculitis in the viral group (p < 0.001; p = 0.04; p = 0.01). Diagnosis of bronchitis and upper RTI were more common in the viral group (p = 0.02; p = 0.004).Table 1Baseline characteristics for adult patients Missing Total Viral a Any virus b Other c p-value d values (n = 182) (n = 40) (n = 46) (n = 142) Viral vs. any virus Viral vs. other Demographics Age, mean years ± SD (range)55.9 ± 16.1 (18–88)53.6 ± 16.1 (18–83)53.9 ± 15.9 (18–83)56.6 ± 16.1 (18–88)0.930.30 Female sex, n (%)76 (41.8)14 (35.0)19 (41.3)62 (43.7)0.550.33 Outpatients, n (%)20 (11.0)5 (12.5)5 (10.9)15 (10.6)1.000.92Comorbidities, n (%) Asthma13 (7.1)2 (5.0)4 (8.7)11 (7.7)0.810.85 COPD27 (10.6)5 (12.5)7 (15.2)22 (15.5)0.720.64 Other chronic lung diseasee 26 (14.3)2 (5.0)2 (4.3)24 (16.9)1.000.06 Solid cancerf 25 (13.7)3 (7.5)3 (6.5)22 (15.5)1.000.20 Hematologic malignancy38 (20.9)13 (32.5)15 (32.6)25 (17.6)0.990.04 Organ transplantation13 (7.1)3 (7.5)3 (6.5)10 (7.0)1.001.00 Neutropenia20 (11.0)9 (22.5)9 (19.6)11 (7.7)0.740.03 HIV infection6 (3.3)1 (2.5)2 (4.3)5 (3.5)1.001.00 Diabetes mellitus27 (14.8)6 (15.0)7 (15.2)21 (14.8)0.980.97 Collagen vascular disease/Vasculitis33 (18.1)4 (10.0)5 (10.9)29 (20.4)1.000.13 Systemic steroids49 (26.9)11 (27.5)14 (30.4)38 (26.8)0.770.93 Other Immunosuppressiong 21 (11.5)5 (12.5)6 (13.0)16 (11.3)0.941.00 Chronic renal failure45 (24.7)11 (27.5)13 (28.3)34 (23.9)0.940.65Clinical findings Systolic blood pressure, mmHg, mean ± SD (range)9125 ± 24 (63–207)129 ± 27 (63–207)128 ± 28 (63–207)123 ± 22 (67–197)0.870.17 Heart rate, beats/min, mean ± SD (range)894 ± 20 (51–155)91 ± 19 (51–150)94 ± 19 (51–150)94 ± 20 (56–155)0.470.40 Respiratory rate, breaths/min, mean ± SD (range)13026 ± 9 (10–60)23 ± 8 (12–36)27 ± 13 (12–60)27 ± 10 (10–60)0.390.23 Body temperature, °C, mean ± SD (range)2037.6 ± 1.0 (35.4–42.0)37.5 ± 0.9 (35.6–39.6)37.5 ± 0.9 (35.6–39.6)37.6 ± 1.0 (35.4–42.0)1.000.59Laboratory findingsh, mean ± SD (range) C-reactive protein (maximum), mg/l13151 ± 127 (1–500)159 ± 148 (1–500)166 ± 152 (1–500)148 ± 121 (1–499)0.830.64 White blood cells (maximum), G/l1111.5 ± 10.2 (0.0–97.0)12.2 ± 16.8 (1.8–97.0)12.6 ± 16.3 (1.8–97.0)11.3 ± 7.3 (0.0–41.1)0.910.75 Platelets (minimum), G/l11202 ± 128 (4–713)159 ± 117 (5–513)165 ± 117 (5–513)215 ± 129 (4–713)0.820.02Discharge diagnosis, n (%) Bronchitis22 (12.1)7 (17.5)7 (15.2)15 (10.6)0.780.36 Acute exacerbation of COPD5 (2.7)1 (2.5)1 (2.2)4 (2.8)1.001.00 Upper respiratory tract infection8 (4.4)4 (10.0)4 (8.7)4 (2.8)1.000.14 Respiratory tract infection, unspecified7 (3.8)2 (5.0)4 (8.7)5 (3.5)0.810.96 Community-acquired pneumonia65 (35.7)21 (52.5)25 (54.3)44 (31.0)0.860.01 Hospital-acquired pneumonia12 (6.6)0 (0.0)0 (0.0)12 (8.5) n/a 0.09 Aspiration pneumonia1 (0.5)0 (0.0)0 (0.0)1 (0.7) n/a 1.00 Tuberculosis3 (1.6)0 (0.0)0 (0.0)3 (2.1) n/a 0.95 Otheri 59 (32.4)5 (12.5)5 (10.9)54 (38.0)1.000.002°C, degree Celsius, COPD chronic obstructive pulmonary disease, HIV human immunodeficiency virus, n number, SD standard deviation aCases in which only one or more respiratory viruses were detected bCases in which one or more respiratory viruses were detected (as single or mixed infection) cIncludes bacterial etiology, mixed etiology, no pathogen dFor continuous variables, 2-sample independent t-test was used. For categorical variables, Mantel-Haenszel chi square or Fisher exact test were used eOther chronic lung diseases, e.g. cystic fibrosis, pulmonary sarcoidosis, pulmonary hypertension fAll solid tumors including bronchial carcinoma gPatients with one of the following conditions: primary or secondary antibody deficiency, congenital immunodeficiency, immunosuppressive therapy other than steroids, severe malnutrition with cachexia hHighest/lowest value within a time period of 3 days before and 3 days after date of rtPCR iOther infections (n = 10); neoplastic diseases (n =6); collagen vascular; other rheumatologic or autoimmune (n = 14); sarcoidosis (n = 3); non-infectious non-neoplastic pulmonary diseases (n = 23); cardiovascular diseases (n = 3) Table 2Baseline characteristics for pediatric patients Missing Total Viral a Any virus b Other c p-value d values (n = 72) (n = 40) (n = 45) (n = 32) Viral vs. any virus Viral vs. other Demographics Age, mean years ± SD (range)4.9 ± 5.7 (0–17)4.3 ± 5.4 (0–16)4.7 ± 5.5 (0–16)5.7 ± 6.0 (0–17)0.740.30 Female sex, n (%)31 (43.1)14 (35.0)18 (40.0)17 (53.1)0.640.13 Outpatients, n (%)3 (4.2)2 (5.0)2 (4.4)1 (3.1)1.001.00Comorbidities, n (%) Asthma1 (1.4)1 (2.5)1 (2.2)0 (0.0)1.001.00 Other chronic lung diseasee 13 (18.1)7 (17.5)8 (17.8)6 (18.8)0.970.89 Solid cancerf 1 (1.4)0 (0.0)0 (0.0)1 (3.1) n/a 0.89 Haematologic malignancy10 (13.9)8 (20.0)9 (20.0)2 (6.3)1.000.18 Organ transplantation1 (1.4)1 (2.5)1 (2.2)0 (0.0)1.001.00 Neutropenia9 (12.5)8 (20.0)8 (17.8)1 (3.1)0.790.06 Systemic steroids8 (11.1)5 (12.5)6 (13.3)3 (9.4)0.910.98 Other Immunosuppressiong 3 (4.2)3 (7.5)3 (6.7)0 (0.0)1.000.33Clinical findings Systolic blood pressure, mmHg, mean ± SD (range)29100 ± 18 (59–140)106 ± 15 (71–140)105 ± 14 (71–140)95 ± 18 (59–120)0.820.04 Heart rate, beats/min, mean ± SD (range)3136 ± 33 (60–234)138 ± 32 (60–186)134 ± 32 (60–186)135 ± 35 (72–234)0.580.71 Respiratory rate, breaths/min, mean ± SD (range)1541 ± 20 (16–103)41 ± 21 (18–103)40 ± 21 (16–103)40 ± 19 (16–88)0.840.86 Body temperature, °C, mean ± SD (range)337.6 ± 1.1 (35.0–40.1)37.5 ± 1.1 (35.0–39.5)37.5 ± 1.1 (35.0–39.5)37.7 ± 1.1 (35.1–40.1)1.000.46Laboratory findingsh, mean ± SD (range) C-reactive protein (maximum), mg/l285 ± 141 (5–999)62 ± 77 (5–291)67 ± 81 (5–293)113 ± 191 (7–999)0.780.16 White blood cells (maximum), G/l216.0 ± 12.1 (0.2–63.1)12.6 ± 10.0 (0.2–57.0)13.6 ± 11.3 (0.2–57.0)20.1 ± 13.3 (1.8–63.1)0.680.01 Platelets (minimum), G/l2246 ± 144 (15–674)257 ± 175 (15–674)244 ± 169 (15–674)234 ± 96 (16–488)0.730.49Discharge diagnosis, n (%) Bronchitis10 (13.9)9 (22.5)9 (20.0)1 (3.1)0.780.04 Upper respiratory tract infection14 (19.4)9 (22.5)10 (22.2)5 (15.6)0.980.47 Respiratory tract infection, unspecified4 (5.6)4 (10.0)4 (8.9)0 (0.0)1.000.18 Community-acquired pneumonia15 (20.8)6 (15.0)8 (17.8)9 (28.1)0.730.18 Hospital-acquired pneumonia10 (13.9)5 (12.5)6 (13.3)5 (15.6)0.910.96 Aspiration pneumonia2 (2.8)1 (2.5)2 (4.4)1 (3.1)1.001.00 Otheri 17 (23.6)6 (15.0)6 (13.3)11 (34.4)0.830.06°C, degree Celsius, COPD chronic obstructive pulmonary disease, HIV human immunodeficiency virus, n number, SD standard deviation aCases in which only one or more respiratory viruses were detected bCases in which one or more respiratory viruses were detected (as single or mixed infection) cIncludes bacterial etiology, mixed etiology, no pathogen dFor continuous variables, 2-sample independent t-test was used. For categorical variables, Mantel-Haenszel chi square or Fisher exact test were used eOther chronic lung diseases, e.g. cystic fibrosis, pulmonary sarcoidosis, pulmonary hypertension fAll solid tumors including bronchial carcinoma gPatients with one of the following conditions: primary or secondary antibody deficiency, congenital immunodeficiency, immunosuppressive therapy other than steroids, severe malnutrition with cachexia hHighest/lowest value within a time period of 3 days before and 3 days after date of rtPCR iOther infections (n = 14); neoplastic diseases (n = 1); collagen vascular; other rheumatologic or autoimmune (n = 1); gastroesophageal diseases (n = 1) Table 3Baseline characteristics for all patients Missing Total Viral a Any virus b Other c p-value d values (n = 254) (n = 80) (n = 91) (n = 174) Viral vs. any virus Viral vs. other Demographics Age, mean years ± SD (range)41.5 ± 26.9 (0–88)29.0 ± 27.5 (0–83)29.6 ± 27.4 (0–83)47.2 ± 24.7 (0–88)0.89<0.001 Female sex, n (%)107 (42.1)28 (35.0)37 (40.7)79 (45.4)0.450.12 Children, n (%)72 (28.3)40 (50.0)45 (49.5)32 (18.4)0.94<0.001 Outpatients, n (%)23 (9.1)7 (8.8)7 (7.7)16 (9.2)0.800.91Comorbidities, n (%) Asthma14 (5.5)3 (3.8)5 (5.5)11 (6.3)0.870.61 COPD27 (10.6)5 (6.3)7 (7.7)22 (12.6)0.710.13 Other chronic lung diseasee 39 (15.4)9 (11.3)10 (11.0)30 (17.2)0.960.22 Solid cancerf 26 (10.2)3 (3.8)3 (3.3)23 (13.2)1.000.02 Haematologic malignancy48 (18.9)21 (26.3)24 (26.4)27 (15.5)0.990.04 Organ transplantation14 (5.5)4 (5.0)4 (4.4)10 (5.7)1.001.00 Neutropenia29 (11.4)17 (21.3)17 (18.7)12 (6.9)0.68<0.001 HIV infection6 (2.4)1 (1.3)2 (2.2)5 (2.9)1.000.77 Diabetes mellitus27 (10.6)6 (7.5)7 (7.7)21 (12.1)0.960.28 Collagen vascular disease/Vasculitis33 (13.0)4 (5.0)5 (5.5)29 (16.7)1.000.01 Systemic steroids57 (22.4)16 (20.0)20 (22.0)41 (23.6)0.750.53 Other Immunosuppressiong 24 (9.4)8 (10.0)9 (9.9)16 (9.2)0.980.84 Chronic renal failure45 (17.7)11 (13.8)13 (14.3)34 (19.5)0.920.26Clinical findings Systolic blood pressure, mmHg, mean ± SD (range)38120 ± 25 (59–207)121 ± 26 (63–207)119 ± 26 (63–207)119 ± 24 (59–197)0.670.60 Heart rate, beats/min, mean ± SD (range)11106 ± 31 (51–234)114 ± 35 (51–186)114 ± 33 (51–186)102 ± 28 (56–234)1.000.01 Respiratory rate, breaths/min, mean ± SD (range)14534 ± 18 (10–103)37 ± 21 (12–103)37 ± 20 (12–103)32 ± 15 (10–88)1.000.17 Body temperature, °C, mean ± SD (range)2337.6 ± 1.0 (35.0–42.0)37.5 ± 1.0 (35.0–39.6)37.5 ± 1.0 (35.0–39.6)37.6 ± 1.0 (35.1–42.0)1.000.48Laboratory findingsh, mean ± SD (range) C-reactive protein (maximum), mg/l15132 ± 134 (1–999)111 ± 127 (1–500)117 ± 132 (1–500)141 ± 137 (1–999)0.770.11 White blood cells (maximum), G/l1312.8 ± 11.0 (0.0–97.0)12.4 ± 13.8 (0.2–97.0)13.1 ± 14.0 (0.2–97.0)13.1 ± 9.4 (0.0–63.1)0.750.69 Platelets (minimum), G/l13215 ± 134 (4–713)208 ± 156 (5–674)204 ± 149 (5–674)218 ± 123 (4–713)0.870.62Discharge diagnosis, n (%) Bronchitis32 (12.6)16 (20.0)16 (17.6)16 (9.2)0.690.02 Acute exacerbation of COPD5 (2.0)1 (1.3)1 (1.1)4 (2.3)1.000.99 Upper respiratory tract infection22 (8.7)13 (16.3)14 (15.4)9 (5.2)0.880.004 Respiratory tract infection, unspecified11 (4.3)6 (7.5)8 (8.8)5 (2.9)0.760.18 Community-acquired pneumonia80 (31.5)27 (33.8)33 (36.3)53 (30.5)0.730.60 Hospital-acquired pneumonia22 (8.7)5 (6.3)6 (6.6)17 (9.8)0.930.36 Aspiration pneumonia3 (1.2)1 (1.3)2 (2.2)2 (1.1)1.001.00 Tuberculosis3 (1.2)0 (0.0)0 (0.0)3 (1.7)n/a0.64 Otheri 76 (29.9)11 (13.8)11 (12.1)65 (37.4)0.75<0.001°C, degree Celsius, COPD chronic obstructive pulmonary disease, HIV human immunodeficiency virus, n number, SD standard deviation aCases in which only one or more respiratory viruses were detected bCases in which one or more respiratory viruses were detected (as single or mixed infection) cIncludes bacterial etiology, mixed etiology, no pathogen dFor continuous variables, 2-sample independent t-test was used. For categorical variables, Mantel-Haenszel chi square or Fisher exact test were used eOther chronic lung diseases, e.g. cystic fibrosis, pulmonary sarcoidosis, pulmonary hypertension fAll solid tumors including bronchial carcinoma gPatients with one of the following conditions: primary or secondary antibody deficiency, congenital immunodeficiency, immunosuppressive therapy other than steroids, severe malnutrition with cachexia hHighest/lowest value within a time period of 3 days before and 3 days after date of rtPCR iOther infections (n = 24); neoplastic diseases (n = 7); collagen vascular; other rheumatologic or autoimmune (n = 15); sarcoidosis (n = 3); non-infectious non-neoplastic pulmonary diseases (n = 23); cardiovascular diseases (n = 3); gastroesophageal diseases (n = 1)