Characteristics of study subjects at baseline by study cohort
| Patient characteristics | Specialist cohort | Event cohort |
| Subjects n | 8581 | 52 010 |
| Demographics and lifestyle variables | ||
| Age years, mean±sd | 60.0±14.3 | 55.5±16.2 |
| Female sex | 5730 (66.8) | 35 855 (68.9) |
| Ethnicity | ||
| White | 4339 (50.6) | 22 460 (43.2) |
| Black | 790 (9.2) | 5826 (11.2) |
| Hispanic | 2167 (25.3) | 16 656 (32.0) |
| Asian/Pacific Islanders | 1093 (12.7) | 5810 (11.2) |
| Others/multiple/unknown | 192 (2.2) | 1258 (2.4) |
| Family education ≤grade 12 (%) geocoded | 15.9 (13.1) | 18.3 (14.0) |
| Years of health plan enrolment, mean±sd | 21.0±10.7 | 19.7±10.4 |
| Medical insurance (mutually inclusive) | ||
| Commercial | 4730 (55.1) | 32 095 (61.7) |
| Medi-CAL# | 260 (3.0) | 2932 (5.6) |
| Medicare | 3391 (39.5) | 16 479 (31.7) |
| Private pay | 2319 (27.0) | 11 566 (22.2) |
| Smoking status (based on the last measure prior to the index date) | ||
| Current | 203 (2.4) | 3041 (5.8) |
| Passive | 62 (0.7) | 398 (0.8) |
| Quit | 2659 (31.0) | 15 412 (29.6) |
| Never | 5652 (65.9) | 33 057 (63.6) |
| Unknown | 5 (0.1) | 102 (0.2) |
| BMI¶, mean±sd | 29.1±6.3 | 29.7±7.0 |
| BMI category¶ | ||
| Underweight (<18.5 kg·m−2) | 124 (1.4) | 798 (1.5) |
| Normal weight (18.5–24.9 kg·m−2) | 2211 (25.8) | 12 698 (24.4) |
| Overweight (25–29.9 kg·m−2) | 2957 (34.5) | 16 751 (32.2) |
| Obese (≥30 kg·m−2) | 3279 (38.2) | 21 622 (41.6) |
| Unknown (BMI missing) | 10 (0.1) | 141 (0.3) |
| Comorbidities | ||
| Charlson Comorbidity Index (weighted), mean±sd | 1.5±1.7 | 1.4±1.7 |
| Gastro-oesophageal reflux | 3631 (42.3) | 14 670 (28.2) |
| Asthma | 2688 (31.3) | 15 391 (29.6) |
| COPD clinical diagnosis | 1028 (12.0) | 5623 (10.8) |
| Allergic rhinitis | 2904 (33.8) | 13 814 (26.6) |
| Chronic rhinitis | 2696 (31.4) | 8129 (15.6) |
| Post-nasal drip (upper airway cough syndrome) | 1715 (20.0) | 5526 (10.6) |
| Chronic sinusitis | 2137 (24.9) | 15 056 (28.9) |
| Obstructive sleep apnoea | 646 (7.5) | 3172 (6.1) |
| Pneumonia and influenza and other acute lower respiratory functions | 1599 (18.6) | 13 190 (25.4) |
| Anxiety | 1418 (16.5) | 10 211 (19.6) |
| Depression | 1642 (19.1) | 10 876 (20.9) |
| Potential cough complications | ||
| Costochondritis | 152 (1.8) | 1255 (2.4) |
| Subconjunctival haemorrhage | 94 (1.1) | 554 (1.1) |
| Stress incontinence | 492 (5.7) | 3515 (6.8) |
| Sleep disturbance | 805 (9.4) | 5009 (9.6) |
| Vomiting | 71 (0.8) | 543 (1.0) |
| Rib fracture | 41 (0.5) | 228 (0.4) |
| Any complication | 1513 (17.6) | 10 112 (19.4) |
| Healthcare utilisation | ||
| Any event ≥1 ED visit | 2367 (27.6) | 18 108 (34.8) |
| Any event ≥1 hospitalisation | 757 (8.8) | 6541 (12.6) |
| ED visit with a respiratory dx+ | 992 (11.6) | 7786 (15.0) |
| Hospital admission with a respiratory dx+ | 424 (4.9) | 3743 (7.2) |
| Clinic encounters with a respiratory dx+, mean±sd | 2.95±3.05 | 2.61±2.89 |
| Clinic encounters with a chronic cough dx, mean±sd | 0.485±0.98 | 0.169±0.64 |
| Non-urgent care clinic encounters with a chronic cough dx, mean±sd | 0.468±0.96 | 0.164±0.63 |
| Urgent care clinic encounters with a chronic cough dx, mean±sd | 0.017±0.14 | 0.005±0.08 |
| Specialist visits | ||
| Pulmonologist | 5566 (64.9) | 9317 (17.9) |
| Allergist | 3017 (35.2) | 6218 (12.0) |
| Head and neck surgery | 2101 (24.5) | 7943 (15.3) |
| Gastroenterology | 1468 (17.1) | 7506 (14.4) |
| Urology | 666 (7.8) | 3808 (7.3) |
| Outpatient pharmacy dispensing (all oral) | ||
| Narcotics, no codeine | 2827 (32.9) | 18 770 (36.1) |
| Narcotics, including codeine | 5251 (61.2) | 37 334 (71.8) |
| Codeine | 3947 (46.0) | 29 989 (57.7) |
| Antitussives, including codeine | 4993 (58.2) | 36 100 (69.4) |
| Antitussives, no codeine | 2776 (32.4) | 16 679 (32.1) |
Data are presented as n (%) unless otherwise stated. BMI: body mass index; ED: emergency department; dx: diagnosis. #: Medi-CAL or other state programmes; ¶: last measure prior to the index date; +: refer to supplementary table S3 for the definition of respiratory dx. Chronic cough dx was not included in the list of respiratory dx.