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Coronavirus Disease 2019

Clinical Diagnosis

Incubation Period

The incubation period for COVID-19 is thought to extend to 14 days following exposure, with a median time of 4 to 5 days from exposure to symptom onset. 

Clinical Presentation

The initial presenting signs and symptoms of COVID-19 vary. Over the course of the disease, many symptomatic patients develop an influenza-like illness with fever and lower respiratory tract symptoms. Atypical presentations occur often, and older adults and persons with medical co-morbidities may have delayed presentation of fever and respiratory symptoms. Asymptomatic infections are common.

Symptoms commonly reported among people with COVID-19 include:

  • Fever or chills
  • Cough
  • Shortness of breath or difficulty breathing
  • New loss of taste or smell
  • Sore throat
  • Myalgias
  • Nasal congestion or runny nose
  • Nausea/vomiting
  • Diarrhea
  • Fatigue
  • Headache

Various other symptoms have been associated with COVID-19. While many of the symptoms are common to other respiratory or viral illnesses, new loss of smell or taste appears to be more specific to COVID-19.

Risk for severe disease from COVID-19

Age is a strong risk factor for severe illness, complications, and death. In addition, persons with underlying medical conditions are at higher risk for more severe outcomes from COVID-19.

See CDC Interim Clinical Guidance for Management of Patients with Confirmed Coronavirus Disease for a more detailed discussion of COVID-19 presentations and clinical progression in adults and risk factors for severe disease.


Signs or symptoms of COVID-19 in children include:

  • Fever
  • Fatigue
  • Headache
  • Myalgia
  • Cough
  • Nasal congestion or rhinorrhea
  • New loss of taste or smell
  • Sore throat
  • Shortness of breath or difficulty breathing
  • Abdominal pain
  • Diarrhea
  • Nausea or vomiting
  • Poor appetite or poor feeding

Children infected with SARS-CoV-2 may have many of these non-specific symptoms, may only have a few (such as only upper respiratory symptoms or only gastrointestinal symptoms), or may be asymptomatic. The most common symptoms in children are cough and/or fever.

See CDC Information for Pediatric Healthcare Providers for more information.

Multisystem Inflammatory Syndrome in Children (MIS-C)

Rarely, children infected with COVID-19 may present weeks later with Multisystem Inflammatory Syndrome in Children (MIS-C) – a serious condition with fever, laboratory evidence of inflammation and multiorgan involvement. For more information see the CDC and LAC DPH MIS-C webpages.

Infectious Period

The period of infectiousness for COVID-19 is still being evaluated. Available data indicate that most persons with COVID-19 are infectious approximately 2 days prior to symptom onset until 10 days after symptom onset. Persons with more severe to critical illness or severe immunocompromise likely remain infectious no longer than 20 days after symptom onset. See CDC Duration of Isolation and Precautions for Adults with COVID-19.

For isolation and quarantine purposes, asymptomatic people who test positive for COVID-19 are regarded as being infectious from 2 days before until 10 days after the date of their first positive test. See Isolation and Quarantine.


The understanding of SARS CoV-2 transmission is incomplete and continues to evolve.

The primary means of transmission appears to be between people who have close contact (less than 6 feet apart). When an infected person coughs, sneezes, or talks, respiratory droplets containing virus are released and can infect another person if they make direct contact with mucous membranes (e.g., mouths, noses, eyes) or are inhaled.

There is also evidence that, under certain conditions, droplets and airborne particles can remain suspended in the air and be breathed in by others more than 6 feet away. In general, indoor environments with poor ventilation increase this risk especially if there is heavy breathing (e.g., while singing, chanting, exercising). Infection may also occur through aerosols produced during procedures (such as intubation or cardio-pulmonary resuscitation). 

It may be possible that a person could become infected after touching a surface or object that has the virus on it and then touching one’s mouth, nose, or eyes, but this is not thought to be the primary way the virus spreads.

For CDC patient-friendly information, see How COVID-19 Spreads.

COVID-19 Risk Assessment & Presumptive Clinical Diagnosis

In order to determine the likelihood of COVID-19 infection in a patient, clinicians should assess exposure risk as well as clinical presentation. Providers should have a high index of suspicion for COVID-19 in symptomatic patients with recent high-risk exposures.

COVID-19 Risk Assessment

In the past 2 weeks has the patient had any of the following high-risk exposures:

  • Been exposed to someone confirmed* or suspected to have COVID-19.
  • Worked or lived in a place where one or more people have been diagnosed with COVID-19.
  • Worked in a crowded place or had frequent interactions with many other people (e.g. customers or co-workers) where proper face covering/masking, safe distancing, and other job-specific protective measures were not universally and consistently maintained. The risk is higher if the work is indoors.
  • Lived or slept in a place with other non-household members where safe distancing and proper face covering/masking were not universally and consistently maintained (e.g. shelter, jail, hostel, dormitory, etc.).
  • Participated in high-risk activities such as large gatherings particularly indoors (e.g. weddings, funerals, parties) or travel (especially multiple layovers/stops, cruise ships, or other prolonged mass transit).
  • Had frequent exposures to the any of the 3 C’s without universal and consistent face covering/masking of both the nose and mouth and safe distancing (Confined spaces, Crowds, or Close contact with many other people).

* Patients who report being a close contact to a laboratory confirmed case or who have traveled outside of California within the past 2 weeks are considered the highest risk for infection and are under mandatory quarantine unless they test positive for SARS-CoV-2 virus (and then they are under mandatory isolation). View Quarantine for more information.

Presumptive Clinical Diagnosis

Healthcare providers should make a presumptive diagnosis of COVID-19 in patients with compatible symptoms and no clear alternate diagnosis, especially if they have high risk exposures. The patient should be given isolation orders and instructions without waiting for laboratory confirmation (see isolation action steps for providers).

  • If the healthcare provider reassesses the initial presumptive diagnosis and concludes that the patient is not infected with SARS-CoV-2 (for example, a clear alternate diagnosis was found and the COVID-19 PCR test result is negative) the patient can be released from isolation after they have been fever-free for 24 hours.

See Provider Isolation and Quarantine website for more information.

Lab Testing

SARS CoV-2 diagnostic (viral) testing is recommended for patients with signs or symptoms suggestive of COVID-19. In addition, testing is recommended for asymptomatic persons who are part of an outbreak, who are close contacts to a case, or who live or work in a high-risk setting. See LAC DPH Testing Guidelines .

Note: viral testing is not recommended for asymptomatic persons who have recently recovered from laboratory confirmed COVID-19 within the past 90 days. See Patients with a History of Recent Recovery from COVID-19 for more information.

When ordering diagnostic viral tests please make sure to confirm the patient’s current phone number(s) and address and include it in the laboratory requisition to facilitate prompt contact tracing if the result is positive.

Symptomatic patients should be advised to self-isolate pending test results.

Visit COVID-19 Provider Testing Hub for information on SARS-CoV-2 tests, FAQs, LAC DPH Testing Guidelines, and local testing resources.

When a patient tests positive for SARS-CoV-2 virus
  • Provide blanket isolation orders and instructions (if they were not already given) as outlined in the isolation action steps for providers.
  • Inform them that LA County Public Health will attempt to call them to interview them for contact tracing. Please encourage them to answer or return Public Health’s calls.
  • Confirm the patient’s current phone number(s) and address and include it in the Medical Provider COVID-19 Report Form which should be submitted within one day.
Additional COVID-19 Resources

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