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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.

Post-COVID Conditions

Some people experience new, recurring, or ongoing symptoms four or more weeks after infection or initial symptom recovery. These long-term effects go by many names (e.g., post-COVID conditions, long COVID, long-haul COVID, post-acute COVID-19) and can develop even in patients who had asymptomatic or mild infections.

See CDC Post-COVID Conditions: Information for Healthcare Providers.

Infectious Period

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 likely remain infectious no longer than 20 days after symptom onset. However, there have been several reports of people with severe immunocompromise shedding replication competent virus beyond 20 days. 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.


There are three principal ways in which infectious exposures to respiratory fluids carrying SARS-CoV-2 occur:

  1. Inhalation of aerosol particles and small droplets. The concentration of these small droplets is generally highest within three to six feet of an infected person. However, these small particles can remain airborne, posing a risk at a greater distance in enclosed spaces.
  2. Deposition of virus in larger exhaled droplets and particles onto mucous membranes. Risk of transmission is highest close to an infected person and decreases with distance.
  3. Touching mucous membranes with hands contaminated by exhaled respiratory fluids or by fomites. Note: Fomite transmission likely does not cause a substantial percentage of infections.
Inhalation plays a larger role than previously believed, as aerosolized particles can remain in the air for minutes to hours. This is more likely in enclosed spaces with poor ventilation, especially if an infectious person spends an extended period in that space or if they are participating in activities that increase exhalation of respiratory fluids, such as vigorous exercise, singing, or shouting.

Read CDC’s Scientific Brief: SARS-CoV-2 Transmission.

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 who are not fully vaccinated against COVID-19.

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 masking, physical distancing, and/or 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 crowded enclosed place with other non-household members with unknown vaccination status (e.g., shelter, jail, hostel, dormitory, etc.).

* Patients who are not fully vaccinated and report being a close contact to a laboratory confirmed case 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 diagnostic viral testing was not performed or the patient has a negative viral test result, but the suspicion for COVID-19 remains high, the patient should continue isolation as a presumptive case pending confirmatory testing. See FAQ What if I am concerned about a result being a false negative.
  • 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.

Diagnostic SARS-CoV-2 Testing

SARS CoV-2 diagnostic (viral) testing is recommended for patients with signs or symptoms suggestive of COVID-19 regardless of vaccination status.

Post-exposure testing (i.e., they are close contacts to a confirmed case or are part of an outbreak investigation) of asymptomatic persons is recommended for patients that are not fully vaccinated. Testing of fully vaccinated asymptomatic persons who were exposed in a high-risk congregate setting or are part of an outbreak investigation may be warranted. See LAC DPH Testing Guidelines .

Note: Viral testing is not recommended for persons who have recently recovered from laboratory confirmed COVID-19 within the past 90 days. This is because recently infected persons are known to shed non-infectious viral particles for at least 90 days after recovery and because re-infection is unlikely to occur during this period. If a patient develops new symptoms consistent with COVID-19 ≤ 90 days from the initial positive viral test, if an alternate etiology cannot be identified, then retesting may be considered in consultation with infectious disease specialists or public health. See Patients with a History of Recent Recovery from COVID-19 for more information.

When ordering diagnostic 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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