Table 1.
Baseline characteristics
| Clarithromycin n=52 251 | Azithromycin n=46 618 | Standardised differences* | |
|---|---|---|---|
| Demographics | |||
| Age, years, median (IQR) | 71 (68–77) | 71 (68–77) | |
| Women, n (%) | 27 932 (53.5) | 25 682 (55.1) | 0.03 |
| Income quintile | |||
| First (lowest) | 8951 (17.1) | 7706 (16.5) | 0.02 |
| Second | 10 447 (20.0) | 8899 (19.1) | 0.02 |
| Third (middle) | 10 153 (19.4) | 8937 (19.2) | 0.01 |
| Fourth | 10 822 (20.7) | 9633 (20.7) | 0 |
| Fifth (highest) | 11 703 (22.4) | 11 285 (24.2) | 0.04 |
| Year of cohort entry†, n (%) | |||
| 2003–2005 | 21 369 (40.9) | 18 979 (40.7) | 0.01 |
| 2006–2008 | 19 236 (36.8) | 17 198 (36.9) | 0.01 |
| 2009–2010 | 11 646 (22.3) | 10 441 (22.4) | 0.01 |
| Comorbidities, n (%) | |||
| Cancer | 12 733 (24.4) | 11 473 (24.6) | 0.01 |
| Chronic kidney disease‡ | 644 (1.2) | 566 (1.2) | 0 |
| Coronary artery disease§ | 7531(14.4) | 6956 (14.9) | 0.01 |
| Diabetes mellitus¶ | 855 (1.6) | 816 (1.8) | 0.01 |
| Heart failure | 1656 (3.2) | 1536 (3.3) | 0.01 |
| Peripheral vascular disease | 175 (0.3) | 176 (0.4) | 0.01 |
| Stroke/transient ischaemic attack | 246 (0.5) | 249 (0.5) | 0.01 |
| Medication use in the prior 6 months, n (%) | |||
| ACE inhibitors or ARBs | 2769 (5.3) | 2543 (5.5) | 0.01 |
| β blockers | 1787 (3.4) | 1720 (3.7) | 0.01 |
| Potassium sparing diuretics | 461 (0.9) | 389 (0.8) | 0.01 |
| Loop diuretics | 103 (0.2) | 120 (0.3) | 0.01 |
| NSAIDs (excluding ASA) | 2483 (4.8) | 2389 (5.1) | 0.02 |
| Thiazide diuretics | 3479 (6.7) | 3171 (6.8) | 0.01 |
| Cause of infection, n (%) | |||
| Genitourinary infection | 261 (0.5) | 265 (0.6) | 0.01 |
| Oropharyngeal infection | 839 (1.6) | 1,000 (2.1) | 0.04 |
| Respiratory infection | 22 084 (42.3) | 17 503 (37.5) | 0.10 |
| Sinus infection | 4,000 (7.7) | 3,178 (6.8) | 0.03 |
| Skin infection | 659 (1.3) | 320 (0.7) | 0.06 |
| Missing | 27 843 (53.3) | 22 266 (47.8) | 0.11 |
| Cultures**, n (%) | |||
| Blood | 28 (0.1) | 21 (0.0) | 0 |
| Genitourinary | 26 (0.0) | 69 (0.01) | 0.03 |
| Gynaecology | 120 (0.2) | 134 (0.3) | 0.01 |
| Sputum | 127 (0.2) | 75 (0.2) | 0.02 |
| Urine | 1,090 (2.1) | 931 (2.0) | 0.01 |
| Concurrent medication prescription, n (%) | |||
| Inhaled steroids | 28 (0.1) | 31 (0.1) | 0.01 |
| Bronchodilators | 1202 (2.3) | 929 (2.0) | 0.02 |
| Main specialty of prescribing physician, n (%) | |||
| GP/FP | 39 743 (76.1) | 34 308 (73.6) | 0.06 |
| Internal medicine | 280 (0.5) | 260 (0.6) | 0.01 |
| General surgery | 100 (0.2) | 151 (0.3) | 0.02 |
| Other | 1148 (2.2) | 1042 (2.2) | 0 |
| Missing | 10 980 (21.0) | 10 857 (23.3) | 0.06 |
Data presented as number (per cent), except for age, which is presented as mean (SD).
*Standardised differences are less sensitive to sample size than traditional hypothesis tests. They provide a measure of the difference between groups divided by the pooled SD; a value greater than 10% (0.1) is interpreted as a meaningful difference between the groups.
†The year of cohort entry is also referred to as the index date.
‡Assessed by administrative database codes.
§Coronary artery disease includes the receipt of coronary artery bypass graft surgery, percutaneous coronary intervention and diagnoses of angina.
¶Assessed by the receipt of insulin or oral antihyperglycaemics.
**Cultures recorded within 2 weeks prior to and 1 week after the index date.
ARB, angiotensin II receptor blocker; FP, family practitioner; GP, general practitioner; NSAID, non-steroidal anti-inflammatory.