Dear Editor,
COVID-19 was first reported in December, 2019 in Wuhan, China, and
rapidly spread across the globe 1. It has affected
more than 6.4 million people and has led to the death of over 370
thousand as of June 2, 2020 (www.who.org).
Severely affected patients present fever, dry cough, dyspnea, and
fatigue, which are commonly associated with the development of pneumonia
and acute respiratory distress syndrome (ARDS) 2.
Advanced age, ischemic and congestive heart disease, hypertension,
diabetes, and chronic obstructive pulmonary disease (COPD) are the most
important independent predictors of death 2,3. As with
other infectious diseases affecting the respiratory tract, asthma has
been cited as a potential risk factor for severe COVID-194-6; however, no previous study has addressed this
specific question.
Here, we systematically reviewed all papers published on COVID-19 since
its emergence in December 2019 to May 18, 2020, looking into the
description of asthma as a premorbid condition and its putative
association with severe progression of the disease.
Two authors, NFM and CPJ, independently identified cross-sectional and
longitudinal studies published before May 18, 2020, that reported on the
prevalence of asthma as a premorbid condition of severe COVID-19 by
systematically searching PubMed-NCBI database. We restricted the search
for PubMed-NCBI because COVID-19 is a new medical condition and,
currently, PubMed-NCBI covers more than 90% of MEDLINE providing a
widely accessible biomedical resource 7. For database
searches, language of the article was restricted to English. Search
terms included the following: COVID-19 (COVID, COVID 19) ornCov or novel coronavirus or Sars-Cov-2 in the
title and clinical characteristics or asthma anywhere in
the text. Three authors, EM, EPA, and LAV, resolved eventual
discrepancies by discussion and adjudication.
We found 458 articles that met the initial inclusion search criteria
(Supplementary Figure 1). All articles were assessed by authors and 290
were excluded (Supplementary Table 1) due to one or more of the
following criteria: editorials; metanalyses; systematic reviews;
commentaries; letters to the Editor; no description of patient’s
clinical characteristics or premorbid conditions; and main text in a
language other than English.
The remaining 150 articles were included in the study. Supplementary
Table 2 depicts the details of all articles analyzed. As a whole, the
articles described the clinical aspects of 36,072 COVID-19 patients. One
hundred and seven studies mentioned the existence of other respiratory
premorbidities except for asthma. Asthma was mentioned as a premorbid
condition in only eighteen studies (Table 1). There was a total of 8,690
patients included in the studies mentioning asthma, and 655 patients
were previously diagnosed with asthma. In most of the studies describing
other respiratory illnesses, COPD was the leading diagnosis.
Based on the current medical records, we conclude that 7.5% of patients
included in articles describing the clinical characteristics of COVID-19
patients and citing asthma were previously diagnosed with asthma. If all
studies providing any clinical description of COVID-19 comorbidities are
taken into consideration, asthma was present in only 1.8% of patients.
These numbers are far less than expected considering the prevalence of
asthma in the world. According to the World Asthma Report
(http://www.globalasthmareport.org), there were as many as 339 million
people living with asthma in the world in 2018, which corresponds to
4.4% of the world’s population.
In conclusion, asthma does not seem to be an important premorbid
condition in COVID-19 patients; or, conversely, it could be a protective
factor, as previously proposed 8. The findings herein
reported could be an epidemiological truth that should be further
explored in mechanistic studies or could be due to the fact that
researchers are not properly investigating and describing the
premorbidities in COVID-19 patients. Whatever the reasons, the medical
community should be aware of the implications of missing the diagnosis
of a potentially severe respiratory disease such as asthma that could
worsen the prognosis of COVID-19 patients.
Acknowledgements. NFM was supported by The São Paulo Research
Foundation (grant: 2016/17810-3), and CPJ was supported by Coordination
for the Improvement of Higher Education Personnel (CAPES) grant: 1744875
and 88882.434715/2019-01. EM, LAV and EPA are supported by grants from
São Paulo Research Foundation (grants: 2013/07607-8 and 2020/) and
Brazilian National Council of Scientific and Technological Development
(CNPq).
Ethics. The study does not require ethical approval because the
systematic review is based on published research and the original data
are anonymous.