Table 1.
Demographic characteristics of the study population.
| Total (N = 761) | Test-negative controls (n = 200) | Test-positive cases (n = 561) | |
|---|---|---|---|
| Age at hospitalisation, years | 60.0 (44.0–69.0) | 63.0 (49.0–69.2) | 58.0 (43.0–69.0) |
| 18–49 | 248 (32.6) | 53 (26.5) | 195 (34.8) |
| 50–64 | 225 (29.6) | 54 (27.0) | 171 (30.5) |
| ≥65 | 288 (37.8) | 93 (46.5) | 195 (34.8) |
| Sex | |||
| Female | 323 (42.4) | 78 (39.0) | 245 (43.7) |
| Male | 438 (57.6) | 122 (61.0) | 316 (56.3) |
| Country/Study contributora | |||
| Austria/Klinik Favoriten | 79 (10.4) | 2 (1.0) | 77 (13.7) |
| Belgium | 153 (20.1) | 24 (12.0) | 129 (23.0) |
| St Pierre | 25 (3.3) | 11 (5.5) | 14 (2.5) |
| Universitair Ziekenhuis Antwerpen | 128 (16.8) | 13 (6.5) | 115 (20.5) |
| Italy/CIRI-IT | 131 (17.2) | 36 (18.0) | 95 (16.9) |
| Spain | 398 (52.3) | 138 (69.0) | 260 (46.3) |
| FISABIO | 127 (16.7) | 43 (21.5) | 84 (15.0) |
| Hospital Germans Trias i Pujol | 171 (22.5) | 75 (37.5) | 96 (17.1) |
| Hospital Universitari Vall d'Hebron | 100 (13.1) | 20 (10.0) | 80 (14.3) |
| Body mass index (BMI) category | |||
| Underweight (BMI <18.5) | 6 (0.8) | 1 (0.5) | 5 (0.8) |
| Normal/healthy weight (BMI ≥18.5 to <25.0) | 124 (16.3) | 44 (22.0) | 80 (14.3) |
| Overweight (BMI ≥25.0 to <30.0) | 132 (17.3) | 33 (16.5) | 99 (17.6) |
| Obese (BMI ≥30.0) | 128 (16.8) | 24 (12.0) | 104 (18.5) |
| No information | 7 (0.9) | 1 (0.5) | 6 (1.1) |
| Missing | 364 (47.8) | 97 (48.5) | 267 (47.6) |
| Number of chronic conditions | |||
| 0 | 319 (41.9) | 54 (27.0) | 265 (47.2) |
| 1 | 156 (20.5) | 44 (22.0) | 112 (20.0) |
| 2 | 139 (18.3) | 46 (23.0) | 93 (16.6) |
| ≥3 | 147 (19.3) | 56 (28.0) | 91 (16.2) |
| Excluding immunodeficiency | n = 708 | n = 176 | n = 532 |
| 0 | 319 (45.1) | 54 (30.7) | 265 (49.8) |
| 1 | 147 (20.8) | 41 (23.3) | 106 (19.9) |
| 2 | 118 (16.7) | 37 (21.0) | 81 (15.2) |
| ≥3 | 124 (17.5) | 44 (25.0) | 80 (15.0) |
| Participants with chronic conditionb | |||
| Asthma | 48 (6.3) | 22 (11.0) | 26 (4.6) |
| Lung disease | 138 (18.1) | 63 (32.5) | 75 (13.4) |
| Cardiovascular disease | 166 (21.8) | 63 (32.5) | 103 (18.4) |
| Hypertension | 252 (33.1) | 69 (34.5) | 183 (32.6) |
| Chronic liver disease | 32 (4.2) | 9 (4.5) | 23 (4.1) |
| Chronic kidney disease | 68 (8.9) | 26 (13.0) | 42 (7.5) |
| Type 2 diabetes | 133 (17.5) | 29 (14.5) | 104 (18.5) |
| Cancer | 71 (9.3) | 34 (17.0) | 37 (6.6) |
| Immunodeficiency (or organ transplant) | 53 (7.0) | 24 (12.0) | 29 (5.2) |
| Pregnancy | n = 323 | n = 78 | n = 245 |
| No | 288 (89.2) | 76 (97.4) | 212 (86.5) |
| Yes | 22 (6.8) | 1 (1.3) | 21 (8.6) |
| No information | 10 (3.1) | 1 (1.3) | 9 (3.7) |
| Missing | 3 (0.9) | 0 | 3 (1.2) |
| Prior SARS-CoV-2 infectionc | |||
| No prior infection recorded | 503 (66.1) | 120 (60.0) | 383 (68.3) |
| Yes – clinical diagnosis | 3 (0.4) | 1 (0.5) | 2 (0.4) |
| Yes – laboratory-confirmed | 19 (2.5) | 13 (6.5) | 6 (1.1) |
| No information | 2 (0.3) | 0 | 2 (0.4) |
| Missing | 234 (30.7) | 66 (33.0) | 168 (29.9) |
| Vaccinated for influenza within 12 months prior to SARI hospital admission | |||
| No | 485 (63.7) | 144 (72.0) | 341 (60.8) |
| Yes | 72 (9.5) | 35 (17.5) | 37 (6.6) |
| No information | 185 (24.3) | 19 (9.5) | 166 (29.6) |
| Missing | 19 (2.5) | 2 (1.0) | 17 (3.0) |
| Received any pneumococcal vaccine | |||
| No | 483 (63.5) | 139 (69.5) | 344 (61.3) |
| Yes | 66 (8.7) | 39 (19.5) | 27 (4.8) |
| No information | 194 (25.5) | 20 (10.0) | 174 (31.0) |
| Missing | 18 (2.4) | 2 (1.0) | 16 (2.9) |
| Smoking history | |||
| Never smoked | 258 (33.9) | 47 (23.5) | 211 (37.6) |
| Ex-smoker | 150 (19.7) | 49 (24.5) | 101 (18.0) |
| Occasional smoker | 13 (1.7) | 7 (3.5) | 6 (1.1) |
| Daily smoker | 88 (11.6) | 48 (24.0) | 40 (7.1) |
| No information | 243 (31.9) | 45 (22.5) | 198 (35.3) |
| Missing | 9 (1.2) | 4 (2.0) | 5 (0.9) |
| Long-term care facility resident | |||
| No | 737 (96.8) | 190 (95.0) | 547 (97.5) |
| Yes | 4 (0.5) | 1 (0.5) | 3 (0.5) |
| No information | 11 (1.4) | 5 (2.5) | 6 (1.1) |
| Missing | 9 (1.2) | 4 (2.0) | 5 (0.9) |
| Healthcare worker | |||
| No | 583 (76.6) | 148 (74.0) | 435 (77.5) |
| Yes | 2 (0.3) | 0 | 2 (0.4) |
| No information | 167 (21.9) | 48 (24.0) | 119 (21.2) |
| Missing | 9 (1.2) | 4 (2.0) | 5 (0.9) |
| Period of disease onset | |||
| May–Jun 2021d | 55 (7.2) | 5 (2.5) | 50 (8.9) |
| Jul–Sep 2021 | 142 (18.7) | 32 (16.0) | 110 (19.6) |
| Oct–Dec 2021 | 307 (40.3) | 83 (41.5) | 224 (39.9) |
| Jan–Mar 2022 | 188 (24.7) | 51 (25.5) | 137 (24.4) |
| Apr–Jun 2022 | 55 (7.2) | 24 (12.0) | 31 (5.5) |
| Jul–Aug 2022 | 14 (1.8) | 5 (2.5) | 9 (1.6) |
| Genetic variante | |||
| Alpha | 1 | NA | 1 (0.2) |
| Beta | 1 | NA | 1 (0.2) |
| Delta | 123 | NA | 123 (21.9) |
| Omicron | 86 | NA | 86 (15.3) |
| Not interpretable/unknown | 2 | NA | 2 (0.4) |
| Missing | 348 | NA | 348 (62.0) |
| Vaccinated against COVID-19 | |||
| No | 641 (84.2) | 140 (70.0) | 501 (89.3) |
| Fully vaccinated with two doses of AZD1222 | 120 (15.8) | 60 (30.0) | 60 (10.7) |
| Month and year of second AZD1222 dosef | n = 120 | n = 60 | n = 60 |
| March 2021 | 1 (0.8) | 0 | 1 (1.7) |
| April 2021 | 0 | 0 | 0 |
| May 2021 | 5 (4.2) | 3 (5.0) | 2 (3.3) |
| June 2021 | 33 (27.5) | 19 (31.7) | 14 (23.3) |
| July 2021 | 75 (62.5) | 34 (56.7) | 41 (68.3) |
| August 2021 | 4 (3.3) | 3 (5.0) | 1 (1.7) |
| September 2021 | 2 (1.7) | 1 (1.7) | 1 (1.7) |
Data shown are n (%) or median (IQR).
CIRI-IT = Interuniversity Research Centre on Influenza and Other Transmissible Infections. COVID-19 = coronavirus disease 2019. FISABIO = Fundación para el Fomento de la Investigación Sanitaria y Biomédica. IQR = interquartile range. SARI = severe acute respiratory infection. SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2.
Population demographics, clinical characteristics, and vaccination status of test-negative controls and test-positive cases.
Totals sum to 100% across countries or across Study Contributors; for countries in which there was more than one Study Contributor, indented rows illustrate the numbers of participants from each Study Contributor within that country. The number of test-negative control participants from Austria, Klinik Favoriten, was limited due to logistical problems with accessing patient records.
Participants with >1 chronic condition are included in each relevant category, and so the percentages for all categories sum to >100 within each column.
As there is no linkage to national testing data, information about prior SARS-CoV-2 infection is reliant on hospital records and patient recall.
Although disease onset occurred prior to the study period in some participants, these individuals were hospitalised within the study period.
Cases for which samples were not genetically sequenced are classified as ‘missing’. Cases with sequenced samples but uninterpretable or unknown results are classified as ‘not interpretable/unknown’.
None of the participants completed their two-dose primary series before March 2021 or after September 2021.