TABLE 3.

Predictors of change in respiratory outcomes and QoL between 3 and 6 months after coronavirus disease 2019 (COVID-19) symptom onset

Model	Outcome	Predictor (at 3 months)	Coefficient	95% CI	p-value	Prespecified covariates
1a	DLCO % predicted	Ground glass score	−2.2	−5.9–1.4	0.23	Sex, age, smoking pack-years
		Time	0.8	−0.5–2.0	0.21
		Ground glass score*Time	0.6	0.05–1.2	0.03
1b	DLCO % predicted	Reticulation score	−8.7	−12.1–  −5.4	<0.001	Sex, age, smoking pack-years
		Time	1.2	0.1–2.2	0.03
		Reticulation score*Time	0.6	−0.01–1.25	0.05
1c	DLCO % predicted	Total CT score	−5.3	−8.7–  −1.8	0.003	Sex, age, smoking pack-years
		Time	0.8	−0.5–2.2	0.23
		Total CT score*Time	0.5	−0.04–1.05	0.07
2a	UCSD	Ground glass score	0.8	−3.4–5.0	0.69	Sex, age, smoking pack-years
		Time	−0.2	−2.9–2.5	0.88
		Ground glass score*Time	−0.1	−1.4–1.1	0.87
2b	QoL	Ground glass score	−0.003	−0.05–0.04	0.89	Sex, age, smoking pack-years
		Time	−0.003	−0.02–0.02	0.77
		Ground glass score*Time	0.01	−0.002–0.02	0.15
3a	UCSD	Unexplained dyspnoea	5.16	−7.95–18.3	0.43	Sex, age, smoking pack-years
		Time	−0.45	−1.98–1.08	0.56
		Unexplained dyspnoea*Time	1.01	−2.98–5.01	0.61
3b	QoL	Unexplained dyspnoea	0.01	−0.11–0.13	0.88	Sex, age, smoking pack-years
		Time	0.01	−0.001–0.02	0.07
		Unexplained Dyspnoea*Time	−0.01	−0.04–0.01	0.33

Time was categorised as 3 months (reference) and 6 months from symptom onset. Ground glass, reticulation and total CT scores were continuous variables that were log-transformed to make them normally distributed and to meet model assumptions. Unexplained dyspnoea at 3 months (defined as the presence of a UCSD dyspnoea score >10 with D_LCO % predicted ≥80%) was categorical (present or absent). Time was included as an interaction term to evaluate whether time modified the effect of the primary predictor on the outcome. The primary predictor variables are denoted in bold. Example of Model 1a interpretation: the coefficient of −2.2 for ground glass score indicates that each 1% increase in ground glass score is associated with a 2.2% decrease in D_LCO % predicted. This association is modified by time. At 6 months, for each 1% increase in ground glass, the coefficient will increase by 1.4 (0.8+0.6), which means there will be a 0.8% (−2.2+1.4) decrease in D_LCO % predicted at 6 months compared to a 2.2% decrease at 3 months. D_LCO : diffusing capacity of the lung for carbon monoxide; UCSD: University of California, San Diego shortness of breath questionnaire; QoL: quality of life. Asterisks (*) signify interaction terms.