Prevalence of comorbid asthma in COVID-19 patients

To the Editor:

The article by Li et al¹ titled “Risk factors for severity and mortality in adult COVID-19 inpatients in Wuhan” provides much-needed detail to inform risk assessment in the presence of preexisting comorbidities in such patients. Given the potentially protracted time line for complete eradication of the public health threat from coronavirus disease 2019 (COVID-19), there is an urgent need for such data to clarify the risk to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected patients with asthma, particularly because severe asthma represents a sizable patient group included in public health advice to shield/stay home.² Surprisingly, the authors report a low prevalence of asthma (0.9% [5 of 548]) in patients with COVID-19, markedly lower than in the adult population of Wuhan (6.4%) and hence speculate that there may be a T_H2-mediated reduced susceptibility to COVID-19 in patients with asthma.¹ A recent literature review including an additional 12 predominantly Chinese COVID-19 cohorts/cases (874 patients) showed that asthma was “surprisingly underreported,”³ and entirely absent in a Chinese nationwide analysis of 1590 COVID-19 cases, where a lack of chronic airways disease awareness and lack of community spirometric testing were postulated reasons.⁴

In contrast, a more recent case series from New York of 393 consecutive confirmed COVID-19 admissions documented a rate of asthma of 12.5%, slightly higher than the prevalence of current adult asthma of 10.1% in New York state.^{5 , 6} As a European comparison of asthma prevalence in hospitalized patients with COVID-19, and with local institutional review board approval, we conducted a retrospective study in our 836-bed tertiary referral center in Dublin, Ireland. We assessed the medical records of 193 consecutive admissions who were SARS-CoV-2–positive over a 1-month period and found that 8.8% (17 of 193) had a physician diagnosis of asthma. Although most of these patients with comorbid asthma had a milder inpatient course and none required invasive mechanical ventilation, there was 1 death, related to COVID-19 and other life-limiting comorbidities (Table I ). The herein-reported rate of comorbid asthma diagnosis is higher than that reported by Li et al, and is comparable to the estimated prevalence of current asthma of 7.0% in adults in Ireland.⁷

Table I.

Demographic and clinical characteristics of hospitalized asthma patients with COVID-19

Characteristic	All patients (n = 17)	No pneumonia∗ (n = 10)	Pneumonia (n = 7)
Age (y)	61 (28-86)	58 (28-82)	64 (46-86)
Sex: male/female	9/8	6/4	3/4
Length of hospital stay (d)†	7 (1-34)	4 (1-15)	11 (4-34)
Intensive care admission, no. of patients	1	0	1
Mechanical ventilation, no. of patients	0	0	0
Clinical outcomes
Discharged from hospital	15	10	5
Remains hospitalized	1	0	1
Death	1	0	1

For age, data are expressed as mean (range).

^∗No pneumonia describes the absence of any consolidation on chest radiograph at any stage during admission.

^†Length of stay data are censored at day 34 for 1 patient.

We theorize that the rate of comorbid asthma in our urban center in Ireland reflects the complex interaction of perhaps greater susceptibility to symptomatic COVID-19 in asthma and an increasingly forewarned and engaged patient population with asthma who may have recently improved their asthma medicine adherence and anticipated/better adhered to public health advice than others in advance of widespread community transmission in their geographic region. We suspect that the low comorbid asthma prevalence observed by Li et al is less likely to indicate lower susceptibility to SARS-CoV-2 in asthma, in light of the above emerging data.^{1 , 4 , 5} There remains a need for larger, more detailed epidemiologic and mechanistic studies for clarification to what extent COVID-19 poses a risk to patients of defined asthma severity.