COVID-19 in humans

Updated on May 14, 2020

Symptoms and transmission

COVID-19 causes flu-like symptoms in people, including mild to severe respiratory illness with cough and shortness of breath or difficulty breathing. Other symptoms include fever, chills, repeated shaking with chills, muscle pain, headache, sore throat, and new loss of taste or smell.

Person-to-person spread has been indicated as the primary means of transmission and seems to occur when there is contact with an infected person's bodily secretions, such as saliva or mucus droplets in a cough or sneeze. Some recent studies have suggested that COVID-19 may be spread by people who are not showing symptoms of the disease, so maintaining social distance (about 6 feet) is important to preventing the spread of COVID-19.

Transmission via touching a contaminated surface or object (i.e., a fomite) and then touching the mouth, nose, or possibly eyes is also possible, but appears to be a secondary route. Smooth (non-porous) surfaces (e.g., countertops, door knobs) transmit viruses better than porous materials (e.g., paper money, pet fur). While we know that certain bacteria and fungi can be carried on fur and hair, we have no examples of where viruses have been transmitted by contact with pet hair or skin and, accordingly, no evidence that the virus that causes COVID-19 can spread to people from the skin or fur of pets.

Time between infection and appearance of symptoms (e.g., fever, cough, shortness of breath, chills, muscle pain, headache, sore throat, new loss of taste or smell, sometimes vomiting or diarrhea) in people is approximately two to fourteen days. The COVID-19 quarantine period for people is 14 days from the last date of exposure.

Cases of COVID-19 and instances of community spread are being reported across the United States. People living in or traveling from places where ongoing community spread of SARS-CoV-2 is taking place appear to be at higher risk of exposure, with relative risk dependent on the location. Healthcare workers caring for patients with COVID-19 also have greater risk, as do close contacts of people with COVID-19. And of course, those who regularly interact with the public, such as veterinarians, face higher exposure risk also. In addition, older adults and people who have severe underlying medical conditions like heart or lung disease, diabetes, and chronic kidney or liver disease seem to be at higher risk for developing serious complications from COVID-19.

Testing people for COVID-19

The US Food and Drug Administration (FDA) has authorized multiple tests to diagnose COVID-19 during the current emergency. All of these viral tests identify the virus in samples from the respiratory system (e.g., nasal or nasopharyngeal swabs). Results from some tests are available within minutes, whereas others require that samples be sent to a laboratory, meaning results may be received several days later. In the near future, healthcare providers in most states will begin offering home collection kits, which FDA has authorized for use during the emergency.

Antibody tests look for antibodies to SARS-CoV-2, so a positive result from this test correlates to an individual having previously been infected with the virus. While some antibody tests are currently available from healthcare providers, the performance of these commercially manufactured antibody tests is currently being evaluated by CDC and other federal agencies and that evaluation is anticipated to be completed by mid-May. Also being explored is whether antibodies from infection with SARS-CoV-2 protect against reinfection with the virus and, if so, for how long. The presence of antibodies cannot confirm current infection, because it usually takes one to three weeks to develop antibodies to SARS-CoV-2. Determining current infection requires a test that identifies virus in samples from the upper respiratory tract (e.g., nasopharyngeal swab).

Treating COVID-19

Current clinical management includes the application of infection prevention and control measures, such as separating the patient from other people and pets in the home and aggressive hygiene and disinfection and supportive care, including supplemental oxygen and mechanical ventilatory support when indicated.  Researchers have been studying new drugs and drugs that are already approved for other health conditions as possible treatments for COVID-19 (e.g., remdesivir, hydroxychloroquine and chloroquine, investigational antivirals, immunotherapeutics, host-directed therapies). On May 1, FDA issued an emergency use authorization for the investigational antiviral drug remdesivir for the treatment of suspected or laboratory-confirmed COVID-19 in adults and children hospitalized with severe disease. No immunization against COVID-19 is available.

The FDA continues to work with drug manufacturers, researchers, and other partners to accelerate the development and approval process for COVID-19 treatments. Information on registered clinical trials for COVID-19 in the United States is available at ClinicalTrials.gov and currently the database lists more than 390 drug (including convalescent plasma), device, biologic, and other trials for COVID-19. Scientists around the world are participating in a platform, Randomised Evaluation of COVID-19 Therapy (RECOVERY), that is examining approximately 30 treatments believed to have potential.

Several drugs used in veterinary medicine have attracted attention in the public press as potential treatments for COVID-19. Among them are ivermectin and chloroquine phosphate. Interest  emerged in ivermectin as a potential treatment after Australian scientists demonstrated that a single dose eradicated all genetic material of SARS-CoV-2 growing in cell culture within 48 hours. Additional testing in animals and people is required to determine whether these in vitro results are mirrored in vivo and what dose might be effective in treating the virus, while still being safe to administer to people. FDA has issued a warning accordingly.

There has been similar interest around the use of chloroquine phosphate after a publication was released suggesting some efficacy for its use in treating COVID-19-associated pneumonia in clinical studies. While used to treat malaria and certain other conditions in people, chloroquine phosphate is also available in a different formulation to treat disease in aquarium fish and  at least one person has died from ingesting chloroquine phosphate in that formulation. FDA has issued a warning accordingly.

People should not self-medicate with medications not approved to treat COVID-19 and veterinarians should advise clients accordingly.

Preventing COVID-19

With the exception of the emergency use authorization for remdesivir, there are currently no antiviral drugs recommended or licensed by FDA to treat COVID-19, and there is no immunization available.

Awareness and prevention are important to reducing the spread of COVID-19:

  • The best way to prevent illness is to avoid being exposed to the virus. The virus is thought to spread mainly from person-to-person, including between people who are in close contact with one another (within about 6 feet).
    • Avoid close contact with people who are ill.
    • Some recent studies suggest that COVID-19 may be spread by people who are not showing symptoms, so social distancing (see below) from those not in your household is important, particularly for people who are at higher risk of becoming very ill.
  • Call your physician if you experience a fever and respiratory or gastrointestinal signs of illness.
  • If you are ill, stay at home except to get medical care and call ahead before visiting your doctor. Minimize your contact with other people, including separating yourself from other members of your household who are not ill.
  • Cover your mouth and nose when you cough or sneeze with a tissue, then throw the tissue in the trash.
  • Avoid touching your face, especially your eyes, nose, and mouth.
  • Wash your hands often. Use soap and water, and wash for at least 20 seconds. If soap and water are not available, use hand sanitizer that contains at least 60% alcohol.
  • Practice social distancing
    • CDC recommends keeping a distance of six to 10 feet from other people. There are reports of asymptomatic infections (detection of virus with no development of corresponding symptoms) and pre-symptomatic infections (detection of virus prior to development of symptoms) with SARS-CoV-2, but their role in transmission is not clear.
    • Avoid gathering in public places, including attending or hosting large social gatherings. To reduce exposure, emergency orders on maximum sizes of gatherings have been issued and need to be followed; in most areas, gatherings of more than 10 people are currently prohibited.
    • If considering a small gathering of friends that does not exceed issued limits, be careful that no one is showing symptoms of disease and/or is a close contact of someone who has. Because little is known about transmission during asymptomatic infection and pre-symptomatic infection, gatherings in general pose a risk and virtual gatherings should be seriously considered as an alternative.
    • Seek delivery options if you need to shop, including for necessary items, such as groceries and medication. If you need to shop in-person, minimize shopping time, shop at off-hours when there are likely to be fewer people in the store, and wear a cloth face covering.
    • As difficult as it may be, refrain from visiting people who are in assisted living and nursing facilities; they are among the most vulnerable population. Most facilities have already severely limited or disallowed visitors.
    • Conduct virtual visits with friends and the elderly to stay in touch and support each other.
  • Regularly clean and disinfect objects and surfaces in your home and workplace. A list of products determined by the EPA to be effective for combatting viral pathogens is available from the American Chemistry Council Center for Biocide Chemistries (CBC). Follow manufacturers’ instructions for use of these products, including recommendations of their applicability to particular surfaces. Other options include dilute household bleach (5 tablespoons bleach per gallon of water) and alcohol solutions (at least 70% alcohol).
  • Those living in households with a person ill with COVID-19 should closely monitor their own health and call their healthcare provider right away if they develop symptoms suggestive of COVID-19.
  • CDC recommends the use of cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores, pharmacies), especially in areas of significant community-based transmission. The purpose of the use of face coverings is to slow the spread of the virus and help people who may have SARS-CoV-2 and do not know it from transmitting it to others. The cloth face coverings recommended are not surgical masks or N-95 respirators. Those should continue to be reserved for healthcare workers and other medical first responders. A publication in the Lancet suggests that it would be reasonable that vulnerable individuals avoid crowded areas and use surgical facemasks rationally when exposed to high-risk areas. Facemasks should be used by people with symptoms of COVID-19 to avoid spreading the disease to others and facemasks are also important for healthcare workers and people who are taking care of someone at home or in a healthcare facility.

Guidance is available from the CDC to help you protect those in your household from COVID-19.