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B73 COVID-19

Home Page and Core Information
Procedural Guidance for DPH Staff

COVID-19 – Core Information

  • Agent, Identification, Differential Diagnosis and Diagnosis sections
  • Incubation, Reservoirs, Source, and Transmission sections
  • Communicability/Period of Infectiousness section
  • Determining Close Contacts section
  • Specific Treatment and Immunity section
  • Diagnostic Procedures section
  • Vaccinated Persons section
  • Patients with a History of Recent Recovery from COVID-19 section

B73 COVID Chapters

  • Acute Psychiatric Hospitals webpage
  • Congregate Residential Settings webpage
  • Adult Day Care Centers webpage
  • People Experiencing Homelessness (PEH) webpage
  • Early Care and Education and K-12 Schools webpage
  • Institutes of Higher Education webpage
  • Law Enforcement, Correctional and Detention Facilities webpage
  • Non-Residential Settings webpage
  • Skilled Nursing Facilities webpage


A human coronavirus (SARS-CoV-2) first identified in December 2019 causes COVID-19.


  1. Symptoms:

    Patients with SARS-C0V-2 infection can experience a range of clinical manifestations, from no symptoms to critical illness. Patients who are older or who have underlying medical conditions are at higher risk of progressing to severe COVID-19, especially if they are unvaccinated or under vaccinated.

    Symptoms commonly reported among adults with COVID-19 include:

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

    Signs and symptoms of COVID-19 in children vary by age of the child and are usually milder compared to adults.

    See NIH Clinical Spectrum of SARS-CoV-2 Infection for a more detailed discussion of COVID-19 clinical signs and symptoms including severity of illness categories.

  2. Differential Diagnosis: Other agents that cause febrile respiratory illnesses including, but not limited to, influenza viruses, respiratory syncytial virus, parainfluenza viruses, Streptococcus pneumoniae, Legionella species, mycoplasma, and other atypical pneumonia agents.

  3. Diagnosis:
    CSTE (to be used in outbreak settings and for close contacts)

Case Classification


  • Meets supportive laboratory evidence†† with no prior history of being a confirmed or probable case.

†† For suspect cases, jurisdictions may opt to place them in a registry for other epidemiological analyses or investigate to determine probable or confirmed status.


  • Meets clinical criteria AND epidemiologic linkage with no confirmatory or presumptive laboratory evidence for SARS-CoV-2, OR

  • Meets presumptive laboratory evidence, OR

  • Meets vital records criteria with no confirmatory laboratory evidence for SARS-CoV-2.


  • Meets confirmatory laboratory evidence.

Clinical Criteria

In the absence of a more likely diagnosis:

  • Acute onset or worsening if at least two of the following symptoms or signs:

    • fever (measured or subjective),

    • chills,

    • rigors,

    • myalgia,

    • headache,

    • sore throat,

    • nausea or vomiting,

    • diarrhea,

    • fatigue,

    • congestion or runny nose.


  • Acute onset or worsening of any one of the following symptoms or signs:

    • cough,

    • shortness of breath,

    • difficulty breathing,

    • olfactory disorder,

    • taste disorder,

    • confusion or change in mental status,

    • persistent pain or pressure in the chest,

    • pale, gray, or blue colored skin, lips, or nail beds, depending on skin tone,

    • inability to wake or stay awake.


  • Severe respiratory illness with at least one of the following:

    • Clinical or radiographic evidence of pneumonia,

    • Acute respiratory distress syndrome (ARDS).

Laboratory Criteria

Confirmed laboratory evidence:

  • Detection of SARS-CoV-2 ribonucleic acid (RNA) in a post-mortem respiratory swab OR clinical specimen using a diagnostic molecular amplification test performed by a Clinical Laboratory Improvement Amendments (CLIA)-certified provider, OR
  • Detection of SARS-CoV-2 by genomic sequencing.


Presumptive laboratory evidence:

  • Detection of SARS-CoV-2 specific antigen in a post mortem obtained respiratory swab OR clinical specimen using a diagnostic test performed by a CLIA-certified provider.

Supportive laboratory evidence:

  • Detection of antibody in serum, plasma, or whole blood specific to natural infection with SARS-CoV-2 (antibody to nucleocapsid protein), OR
  • Detection of SARS-CoV-2 specific antigen by immunocytochemistry in an autopsy specimen, OR
  • Detection of SARS-CoV-2 RNA or specific antigen using a test performed without CLIA oversight.



Omicron has a short incubation period. Estimated to be 2-4 days.




Nasal and pharyngeal secretions.


Omicron is very infectious. More transmissible than original SARS-CoV-2 and Delta variant. See ACIP PowerPoint presentation Update on Omicron (12-16-2021)

The information below is based on SARS-CoV-2 variants prior to Omicron.

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 (May 7, 2021).

For CDC patient-friendly information, see How COVID-19 Spreads (July 14, 2021).

Communicability/Period of Infectiousness

CDC has been monitoring the emerging science on when and for how long a person is maximally infectious with Omicron.

Per CDC, SARS-CoV-2 transmission occurs early in the course of infection. Infectiousness peaks around one day before symptom onset and declines within a week of symptom onset, with an average period of infectiousness and risk of transmission between 2-3 days before and 8 days after symptom onset. These data are from studies of prior SARS-CoV-2 variants, including Delta.

 A person with COVID-19 is considered to be infectious beginning 2 days before their symptoms began until their isolation period ends. If they test positive for COVID-19 but remain asymptomatic, they are considered to be infectious from 2 days before the test was collected until their isolation ends.

When isolation can end:

Everyone with COVID-19 must isolate for at least 5 days.

  • Isolation can end after Day 5 ONLY if all of the following criteria are met:

  1. A COVID-19 viral test collected on Day 5 or later is negative

  2. No fever for at least 24 hours without the use of fever reducing medicine

  3. Other symptoms are not present or are improving


  • Isolation can end after Day 10 if both these criteria are met:

  1. No fever for at least 24 hours without the use of fever reducing medicine

  2. Other symptoms are not present or are improving

For the general public see Isolation Instructions for People with COVID-19.

Note: for certain populations where there is an especially low tolerance for post-recovery viral shedding and/or increased risk of infection such as skilled nursing facilities the transmission-based precautions/patient isolation is continued for 15-20 days post initial symptoms/date of test collection).

Severely immunocompromised patients (e.g., currently receiving chemotherapy for cancer, uncontrolled HIV infection with current CD4 <200, prednisone treatment >20mg/kg for more than 14 days) may produce replication-competent virus beyond 20 days and require additional testing and consultation with infectious diseases specialists and infection control experts.

Determining Close Contacts

A close contact is a person with exposure to a laboratory-confirmed or clinical case of COVID-19 during the period of infectiousness of the case (see Communicability/Period of Infectiousness above). This is from 2 days before symptom onset (or date of first positive lab test for asymptomatic persons) until the case meets criteria for discontinuing isolation/transmission-based precautions.

Effective April 15, 2022, a close contact is defined as anyone sharing the same indoor airspace (e.g., home, clinic waiting room, airplane, etc.) for a cumulative total of 15 minutes or more over a 24-hour period (for example, three individual 5-minute exposures for a total of 15 minutes) during an infected person's (laboratory-confirmed or clinical diagnosis) infectious period.

Exception: Cal-OSHA’s Emergency Temporary Standards (ETS) state that employees have not had a close contact if they were wearing a respirator required by the employer and used in compliance with section 5144 of the ETS when they were within six feet of a case during the high-risk exposure period.

Note: Please refer to sector specific guidance regarding the identification of close contacts who may require quarantine or work exclusion. There may be instances where the definition of close contact needs to be further defined by distance or space.

See site specific B73 for more specific guidance on determining close contacts.

For general public, see Instructions for Close Contacts at ph.lacounty.gov/covidcontacts.

Specific Treatment

See the NIH COVID-19 Treatment Guidelines for comprehensive information and the National Institutes of Health have published interim guidelines for the medical management of COVID-19 prepared by the COVID-19 Treatment Guidelines Panel.  Providers should make treatment decisions based on currently available evidence.

Therapeutics are available for patients at high risk for progression to severe disease (e.g., age >65 or age >12 with underlying medical conditions). To be eligible, patients must have mild-moderate symptoms and a positive SARS-CoV-2 viral test result. Treatment must be given within 5 days of symptoms onset.

See LAC DPH Monoclonal & Antiviral Therapy for Non-Hospitalized Patients webpage.


Natural immunity: Natural immunity from prior SARS-CoV-2 viral variants does not appear to be protective against Omicron variant. Among other human coronaviruses, reinfection appears to occur variably over time after onset of infection. The likelihood of re-infection is expected to increase over time because of waning immunity and the possibility of exposure to virus variants. In addition, the level of protection after infection may vary depending on how mild or severe the illness was as well as the person's age.

Vaccine-induced immunity: Currently authorized COVID-19 vaccines remain effective at preventing severe illness, hospitalization, and death against SARS-CoV2 including Omicron.  The primary series for COVID-19 vaccines currently authorized or approved for use in the United States are less effective at preventing infection with the Omicron variant compared to earlier variants and may be somewhat less effective at preventing hospitalization associated with the Omicron variant. A COVID-19 vaccine booster dose, however, increases vaccine effectiveness against SARS-CoV-2 infection and hospitalization, including against the Omicron variant. See CDC COVID-19 Vaccine Effectiveness.

See CDC Science Brief-Immune Response to Infection and Vaccination

Diagnostic Procedures

Clinical and epidemiologic histories are required to aid in diagnosis. Direct viral detection methods with sensitive molecular tests (e.g. RT-PCR) are recommended for diagnosing current infection with SARS-CoV-2. Antigen tests and over the counter (OTC) self-tests can also be used to diagnose acute infection but they are less accurate than PCR tests.

When using lower sensitivity assays (e.g., antigen tests, some molecular tests, OTC self-tests), negative results are considered presumptive and confirmation with RT-PCR is recommended, especially if important for clinical management or infection control.

Serological testing is not a standard part of outbreak investigation.

See LAC DPH Currently Available SARS-CoV-2 Tests for an overview of test types.

Facilities are encouraged to test through a commercial lab. Facilities should follow the specimen collection and pick-up instructions as per the facility’s designated commercial clinical laboratory. They should work directly with the clinical laboratory for all questions regarding specimen collection and transport.

See Laboratories Providing Diagnostic Testing for resources to support organizations identify a laboratory provider that best fits their needs.

PHL SARS CoV-2 PCR Specimen Collection

Upper Respiratory Specimen--for initial diagnostic testing, collect at least one upper respiratory specimen.

Any of the following specimens are acceptable:

  • Nasopharyngeal swab
  • Oropharyngeal swab
  • Combined nasopharyngeal/oropharyngeal swab
  • Nasal swab
    • Nasal mid-turbinate swab
    • Anterior nares swab
  • Combined nasal/oropharyngeal swab
  • Nasopharyngeal wash/aspirate
  • Nasal wash/aspirate

Swabs: Acceptable swab types include synthetic fiber swabs (flocked or spun polyester) with plastic or wire shafts. Do not use calcium alginate swabs or cotton swabs with wooden shafts. Place swab in a minimum of 1-3 mL viral transport media, liquid Amies, or saline.

Aspirates and washes: collect 1.5-3.0 mL in a sterile, leak-proof container.

Lower respiratory tract specimens--may be required for patients presenting with severe disease or fatal cases. Acceptable lower respiratory tract specimens include sputum, bronchoalveolar lavage, tracheal aspirate, pleural fluid, lung swab, or lung biopsy. Collect lower respiratory tract specimens in a sterile, leak-proof container. Lung swab should be submitted in viral transport media. A minimum of 2-3 mL is needed for sputum, lavage and aspirates.

Storage: Refrigerate specimens at 2-8°C and transport on cold pack. If specimen storage exceeds 3 days, freeze specimen at ≤ -70°C and ship on dry ice.

For more information see:

  • Interim Guidelines for Collecting, Handling, and Testing Clinical Specimens from Persons for Coronavirus Disease 2019 Guidelines
  • Collection and Submission of Postmortem Specimens from Deceased Persons with Known or Suspected COVID-19 Guidance

Vaccinated Persons

A person is considered up to date with their COVID-19 vaccines when they have received all recommended doses in the primary series AND have received one booster dose, when eligible. See COVID-19 Vaccine Schedules.

A person is considered fully vaccinated ≥2 weeks following the receipt of a primary vaccine series that is either FDA-authorized or approved or has been listed for use by the WHO.

See CDC Stay Up to Date with Your COVID-19 Vaccines

Patients with a History of Recent Recovery from COVID-19

Individuals who have recovered from laboratory-confirmed* COVID-19, for 90 days after the onset of the initial COVID-19 illness (or date of first positive viral test if they never had symptoms):

  • Those with no current symptoms of COVID-19
    • Testing is not recommended.
    • They do not have to quarantine if exposed as a close contact.
    • They must continue to adhere to all other required protective measures, including, but not limited to, wearing face coverings and other job-specific personal protective equipment, maintaining their physical distance from non-household members, following hand hygiene, and staying home if sick, among other protective measures.
  • Those with symptoms of COVID-19
    • Must self-isolate as per heath officer orders and
    • Consult with a medical provider to determine if they may have been re-infected with SARS-CoV-2 or if their symptoms are caused by another etiology.
    • Testing with antigen test is preferred.
*Lab confirmed=positive molecular or antigen test for SARS-CoV-2.

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Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.

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