Adverse respiratory outcomes among patients with resolved asthma: matched retrospective cohort study

Hywel Jones; Bethan Cumins; Rebecca Cannings-John; Haroon Ahmed

doi:10.3399/BJGP.2023.0271

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Figure 1.
Flow of patients into each cohort. IMD = Index of Multiple Deprivation. Obs = observation.

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How this fits in

Patients with asthma may have a period of remission and be regarded as having ‘resolved asthma’ in their primary care record. Despite resolution of symptoms, patients with resolved asthma may have ongoing respiratory pathophysiology and little is known about their ongoing risk of adverse respiratory events. This study found that patients in UK primary care with a record of resolved asthma have a greater risk of respiratory tract infection and antibiotic use than the general population, but one that is lower than patients with active asthma. Patients with resolved asthma may benefit from a comprehensive respiratory assessment if they present with symptoms of a respiratory tract infection to assess symptom burden, airway obstruction, and the potential value of reinitiating inhaled treatment.

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Table 1.

Descriptive characteristics of the three cohorts

Characteristic	Resolved asthma (n = 16 023)	Active asthma (n = 16 023)	Non-asthma (n = 16 023)
Sex
Male	7303 (45.6)	7303 (45.6)	7303 (45.6)
Female	8720 (54.4)	8720 (54.4)	8720 (54.4)

Age at start FUP, years, mean (SD)	37.06 (20.27)	37.41 (20.24)	37.06 (20.27)

Years of follow-up, mean (SD)	1.99 (1.86)	3.54 (2.58)	2.68 (2.02)

Index of Multiple
Deprivation quintile
1 — most deprived	3854 (24.1)	3695 (23.1)	3849 (24.0)
2	3583 (22.4)	3514 (21.9)	3570 (22.3)
3	3134 (19.6)	3158 (19.7)	3061 (19.1)
4	2876 (17.9)	2961 (18.5)	2893 (18.1)
5 — least deprived	2576 (16.1)	2695 (16.8)	2650 (16.5)

Charlson score^a
0	680 (4.2)	531 (3.3)	14 249 (88.9)
1	13 425 (83.8)	13 582 (84.8)	770 (4.8)
2	744 (4.6)	728 (4.5)	677 (4.2)
3	752 (4.7)	772 (4.8)	168 (1.0)
4	225 (1.4)	223 (1.4)	92 (0.6)
≥5	197 (1.2)	187 (1.2)	67 (0.4)

Smoking status
Non-smoker	9198 (57.4)	9167 (57.2)	7618 (47.5)
Ex-smoker	2528 (15.8)	2726 (17.0)	2128 (13.3)
Current smoker	2736 (17.1)	2864 (17.9)	2744 (17.1)
Missing	1561 (9.7)	1266 (7.9)	3533 (22.0)

Spirometry recorded in observation period, yes	880 (5.5)	310 (1.9)	—

FEV₁ recorded in observation period, yes	910 (5.7)	374 (2.3)	—

Annual asthma review recorded in observation period, yes	3658 (22.8)	11 779 (73.5)	—

↵a Charlson score of 0 indicates no comorbidity. Values are n (%) unless otherwise indicated. FEV₁ = forced expiratory volume in 1 second. FUP = follow-up. SD = standard deviation.

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Table 2.

IRR and 95% CIs for primary and secondary outcomes

Outcome and cohort	Events	Person-time, years	Crude IRR (95% CI)^a	Adjusted IRR (95% CI)^b
Asthma hospital admissions
Active asthma	9904	54 179	Reference	Reference
Resolved asthma	1472	31 965	0.28 (0.26 to 0.31)	0.29 (0.27 to 0.32)

URTI hospital admissions
Non-asthma	63	42 969	Reference	Reference
Active asthma	138	56 741	1.65 (1.19 to 2.30)	0.92 (0.62 to 1.37)
Resolved asthma	63	31 965	1.36 (0.92 to 1.99)	0.89 (0.55 to 1.44)

LRTI hospital admissions
Non-asthma	66	42 969	Reference	Reference
Active asthma	410	56 741	4.52 (3.37 to 6.05)	3.04 (2.22 to 4.18)
Resolved asthma	82	31 965	1.82 (1.22 to 2.72)	1.30 (0.87 to 1.95)

Flu or pneumonia hospital
admission
Non-asthma	123	42 969	Reference	Reference
Active asthma	443	56 741	2.70 (2.13 to 3.41)	1.80 (1.40 to 2.31)
Resolved asthma	122	31 965	1.39 (1.02 to 1.90)	1.08 (0.78 to 1.50)

GP asthma exacerbation consultations
Active asthma	3816	56 741	Reference	Reference
Resolved asthma	108	31 965	0.05 (0.04 to 0.07)	0.05 (0.04 to 0.07)

GP LRTI consultations
Non-asthma	804	42 969	Reference	Reference
Active asthma	6985	56 741	6.19 (5.68 to 6.74)	5.27 (4.79 to 5.78)
Resolved asthma	1489	31 965	2.87 (2.57 to 3.19)	2.34 (2.08 to 2.64)

GP all-cause antibiotic prescriptions
Non-asthma	17 285	42 969	Reference	Reference
Active asthma	63 222	56 741	2.64 (2.54 to 2.73)	2.08 (1.99 to 2.17)
Resolved asthma	20 543	31 965	1.83 (1.75 to 1.91)	1.37 (1.30 to 1.44)

↵a Unadjusted models matched on age and sex with the practice included as a random effect to account for clustering.
↵b Models adjusted for age, sex, Index of Multiple Deprivation, Charlson score, and smoking status (imputed where missing), with the practice included as a random effect. CI = confidence interval. IRR = incidence rate ratio. LRTI = lower respiratory tract infection. URTI = upper respiratory tract infection.

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Table 3.

IRR and 95% CIs for primary and secondary outcomes using stricter definitions of resolved and active asthma

Outcome, cohort	Adjusted IRR (95% CI)^a
Asthma hospital admissions
Active asthma	Reference
Resolved asthma	0.25 (0.23 to 0.28)

URTI hospital admissions
Non-asthma	Reference
Active asthma	0.69 (0.43 to 1.11)
Resolved asthma	0.60 (0.31 to 1.15)

LRTI hospital admissions
Non-asthma	Reference
Active asthma	3.20 (2.30 to 4.46)
Resolved asthma	1.06 (0.66 to 1.71)

Flu or pneumonia hospital admission
Non-asthma	Reference
Active asthma	1.83 (1.42 to 2.37)
Resolved asthma	1.09 (0.75 to 1.58)

GP asthma exacerbation consultations
Active asthma	Reference
Resolved asthma	0.04 (0.03 to 0.06)

GP LRTI consultations
Non-asthma	Reference
Active asthma	5.39 (4.87 to 5.96)
Resolved asthma	2.09 (1.81 to 2.40)

GP all-cause antibiotic prescriptions
Non-asthma	Reference
Active asthma	2.20 (2.10 to 2.30)
Resolved asthma	1.21 (1.13 to 1.28)

↵a Models adjusted for age, sex, Index of Multiple Deprivation, Charlson score, and smoking status (using complete cases only), with the practice as a random effect. CI = confidence interval. IRR = incidence rate ratio. LRTI = lower respiratory tract infection. URTI = upper respiratory tract infection.

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