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Answering physicians’ clinical questions about COVID-19

In this EBM Focus article, the DynaMed editorial team answers ten frequently asked questions about coronavirus disease 2019 (COVID-19). EBM Focus articles provide concise summaries of clinical research most likely to inform clinical practice.

The COVID-19 pandemic is an evolving situation with rapidly changing information. The answers to these questions are accurate as of April 30, 2020. 

1. Once a person has recovered from COVID-19, can they get it again?

While it’s clear that patients infected with COVID-19 develop antibodies to the virus, it remains unclear how long the protection lasts. Very early research in macaque monkeys has shown short-term immunity in primates, but this data has not been peer-reviewed yet. Looking at data from survivors of epidemics like SARS (case fatality 11%, 2002) and MERS (case fatality 39%, 2012) may help us develop a vaccine. Coronaviruses are RNA viruses that mutate rapidly, raising concern that immunity may be temporary (this is the reason why we need yearly flu vaccines).

2. How long can the coronavirus remain viable in the air and on surfaces?

SARS-CoV-2 can remain viable in the air for hours and on surfaces for several days. The median half-life of the virus as aerosolized particles is about an hour, but they can remain viable in the air for several hours. In vitro testing demonstrated that SARS-CoV-2 can last for up to 72 hours on plastic and stainless steel, up to 24 hours on cardboard, and up to 4 hours on copper. What remains unclear is the viral load required for infection — just because viral particles were identified on cardboard, it is still unknown if the virus can then go on to infect the respiratory tract.

3. Many of my patients are asking about cloth masks. What can I tell them about how they compare to surgical masks?

There is little evidence evaluating the use of cloth masks with respect to COVID-19 (estimated size 0.12 microns) specifically. Homemade cloth masks (without filters) may prevent the transmission of some particulate matter but were much less effective than manufactured surgical masks at preventing transmission of influenza. There is some evidence that certain materials are more helpful than others, however, and perhaps a cloth mask with vacuum bag filter could approximate the efficacy of a surgical mask if it came to that. While these types of masks may not protect the wearer to any significant extent, they may decrease the spread of the virus from asymptomatic persons and limit touching of the face.

4. Is it true that COVID-19 transmission will decline with warmer weather?

There is no evidence about whether warm weather will decrease COVID-19 cases, but cases are increasing exponentially in areas of the world that are currently experiencing higher temperatures, such as the American South and Africa. On the other hand, MERS transmission was shown to be partly exacerbated by cold windy weather, and seasonal factors beyond temperature (such as traditional holidays) have been hypothesized to exacerbate the current COVID-19 outbreak.

5. What do we know about how coronavirus affects children?

Data from China suggests that up to 16 percent of infected children can be asymptomatic. Most children will have only mild symptoms, but a small percentage of children, particularly if they have other underlying illnesses, develop more serious illness requiring intensive care. Children have died from COVID-19.

6. Should mothers stop breastfeeding if they have symptoms or test positive for the virus?

Although we do not know all the facts about how SARS-CoV-2 is spread, it does not appear to be present in breastmilk. Mothers with known SARS-CoV-2 infection or who are under investigation should take extra care when breastfeeding, including washing hands, wearing a mask and consider covering the baby with a blanket or towel.

7. Does a negative test rule out a SARS-CoV-2 infection?

Keep pretest probability and prevalence in mind when interpreting the results of COVID-19 testing. Unless the sensitivity of a test is 100% (and current estimates for SARS-CoV-2 are in the 70-80% range), if prevalence is high and likelihood of disease high, a negative test cannot rule out disease. The possibility of a false negative result should be especially considered if the patient’s recent exposures and clinical presentation indicate that COVID-19 is likely. Given the limitations on testing that have been present, the true prevalence of COVID-19 infection is almost certainly an underrepresentation. 

8. Should patients with COVID-19 continue taking their ACE inhibitors or ARB medications?

SARS-CoV-2 does use angiotensin converting enzyme 2 (ACE2) receptors to enter respiratory and cardiac cells. Although animal models showed changes in ACE2 expression with ACE inhibitor and ARB use, there are no clinical studies reporting outcomes related to use of these medications. The AHA/ACC currently recommend continuing ACE inhibitors and ARBs given their proven cardioprotective benefits. In addition, there are proposals to use ARBs as a potential co-treatment for COVID-19.

9. Can patients take ibuprofen safely if they have a COVID-19 infection?

Although bench science suggested that nonsteroidal anti-inflammatory drugs (NSAIDs) may increase ACE2 expression, the currently available evidence suggests ibuprofen and other NSAIDs are safe during COVID-19 infection. Despite initially recommending against NSAIDs, the World Health Organization rescinded that statement and the Public Health Agency of Canada, along with other organizations, continue to recommend this class of drugs for symptomatic and anti-pyretic therapy. 

10. If a patient sits in my waiting room with someone who has COVID-19 symptoms, does it put them at “high risk” of exposure?

People seated in the same waiting room (at least two meters away) as a person with symptomatic COVID-19 are likely to be at low risk of exposure. The Public Health Agency of Canada recommends that any person with a cough or fever should wear a mask to wear while in a waiting area to minimize risk of exposure to others.

For more information, see the topic COVID-19 (Novel Coronavirus) in DynaMed

Original article published on EBSCO Health Notes. Written and edited by:

  • Alan Ehrlich, MD, Executive Editor at DynaMed and Associate Professor in Family Medicine at the University of Massachusetts Medical School;
  • Dan Randall, MD, Deputy Editor for Internal Medicine at DynaMed;
  • Katharine DeGeorge, MD, MS, Associate Professor of Family Medicine at the University of Virginia and Clinical Editor at DynaMed;
  • Terri Levine, PhD, Senior Medical Writer in Obstetrics and Gynecology at DynaMed; and
  • Carina Brown, MD, Assistant Professor at Cone Health Family Medicine Residency.

Do you have a question on COVID-19 or another clinical topic? Contact the Ask a Librarian team to request a literature search.


This material is for informational purposes only. It is not intended to be a substitute for professional medical advice and should not be relied on as health or personal advice. The opinions stated by the authors are made in a personal capacity and do not necessarily reflect those of the Canadian Medical Association and its subsidiaries including Joule.  

About the author(s)

DynaMed is a clinician-focused tool designed to facilitate efficient and evidence-based patient care. Rigorous, daily review of medical literature by physician and specialist staff ensures timely and objective analysis, synthesis and guidance. DynaMed includes drug content from Micromedex, Canadian and international guidelines, and clinical images. CMA members have access to DynaMed, a point-of-care tool, included with their membership ― a tool valued at US$399 a year.