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B73 COVID-19

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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

  • COVID-19 Community Care Facilities 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
  • 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. Omicron is a variant of SARS-CoV-2 that emerged in November 2021. It is notable due to its high transmissibility. Since 2021, multiple Omicron lineages have emerged. The CDC and WHO track SARS-CoV-2 variants for mutations that might lead to therapeutic resistance or reduced vaccine efficacy. For more information visit: https://www.cdc.gov/coronavirus/2019-ncov/variants/index.html.


  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.

Case Classification

Outbreak case classification may differ by sector. Please refer to sector specific COVID-19 guidelines for further information about case classification.


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. Anyone with Omicron infection, regardless of vaccination status or whether or not they have symptoms, can spread the virus to others. Data suggest that Omicron can cause reinfection, even in people who have recovered from COVID-19. See CDC Variants of the Virus.

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.

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 the CDC, the majority of SARS-CoV-2 transmission occurs in the 1-2 days prior to onset of symptoms and the 2-3 days after.

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.

To count the days:

  • Day 0 is the first day of symptoms.

  • If they don’t have symptoms, Day 0 is when the first positive test was collected. If they go on to get symptoms, restart with Day 0 as the first day of symptoms.

Ending isolation:

Isolation may end after Day 5* (i.e., between Day 6-10) if:

  • They have not had a fever for at least 24 hours without the use of fever-reducing medicine AND

  • They don’t have any other symptoms, or symptoms are mild and improving

*Note: LAC DPH strongly recommends that they get a negative test for COVID-19 before ending isolation between Day 6-10. If they do test, it is best to use antigen tests (including self-tests) to lower the risk of false positives.

If your symptoms of COVID-19 are not improving, they must continue to isolate until symptoms are improving or until after Day 10.

If they have a condition that weakens their immune system or if they were severely ill with COVID-19 they might need to stay home for longer than 10 days.

If COVID-19 symptoms return or get worse after ending isolation, they may have COVID-19 rebound.

They should take an antigen test. If they test positive, they need to restart isolation at Day 0.

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.

The order of the State Public Health Officer defines who is a close contact varies based on the size of the shared indoor space:

  • In indoor 400,000 or fewer cubic feet per floor (e.g., home, clinic waiting room, airplane, etc.), a close contact is defined as anyone sharing the same indoor airspace for a cumulative total of 15 minutes or more over a 24-hour period while the case was infectious
  • In large indoor spaces greater than 400,000 cubic feet per floor (such as open-floor-plan offices, warehouses, large retail stores, manufacturing, or food processing facilities), a close contact is defined as someone being within 6 feet for a cumulative total of 15 minutes or more over a 24-hour period while the case was infectious.
  • Spaces that are separated by floor-to-ceiling walls (e.g., offices, suites, rooms, waiting areas, bathrooms, or break or eating areas that are separated by floor-to-ceiling walls) must be considered distinct indoor airspaces.

For additional details see CDPH Order Q&A.

People are considered close contacts regardless of the use of face masks by the case or contact. Exception: Cal/OSHA states that employees are not a close contact if they wore a respirator required by the employer and used in compliance with section 5144, whenever they were sharing the same airspace of the COVID-19 case while they were infectious.

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

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

Specific Treatment

See the ph.lacounty.gov/covidtherapeutics and the NIH COVID-19 Treatment Guidelines for comprehensive information on the medical management of COVID-19 prepared by the COVID-19 Treatment Guidelines Panel. Providers should make treatment decisions based on currently available evidence.

For patient friendly information about COVID treatment please refer to: http://publichealth.lacounty.gov/acd/ncorona2019/medication/.


Natural immunity: Natural immunity from prior SARS-CoV-2 viral variants does not appear to be protective against Omicron subvariants. 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.  While efficacy wanes over time, booster doses restore vaccine efficacy for severe outcomes. 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 CDC Testing for SARS-CoV-2 Infection 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
  • Lung swab

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.

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.

Los Angeles County PHL Test Request Form: http://www.publichealth.lacounty.gov/lab/labforms.htm 

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

Information about the 2023-2024 COVID-19 vaccine will be available soon.

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 all recommended booster doses, when eligible. See COVID-19 Vaccine Schedules.

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

Patients with a History of Recent Recovery from COVID-19

A patient with a history of recent recovery from COVID-19 is defined as a person with a positive viral COVID-19 test within the past 3 months (90 days) who has recovered from the previous infection. Recovered means they are no longer considered infectious (i.e., their isolation period has ended).

If the patient had symptoms with their most recent infection, the 90 days are from the onset of the initial COVID-19 symptoms. If they never had symptoms, then the 90 days are from the date of collection of the first positive viral COVID-19 test.

If the recently recovered person

Is asymptomatic

  • If they they have close contact with a COVID-19 case, they are not required to test, quarantine, nor be restricted from work. They must follow the Instructions for Close Contacts including wearing a highly protective mask around others and monitor their health for 10 days.
  • If they have close contact with a COVID-19 case and their first positive test was:
    • <30 days prior -- no viral testing is generally recommended
    • 31-90 days prior -- antigen testing is recommended

Develops new symptoms consistent with COVID-19 illness

  • Testing with antigen tests is recommended, especially if there is no alternative diagnosis and/or the symptoms developed within 10 days after close contact to a case.
  • They should be instructed to self-isolate pending clinical evaluation and the results of SARS-CoV-2 testing, if performed.


Immunocompetent patients who have recovered from acute COVID-19 infection can continue to have detectable SARS-CoV-2 RNA in upper respiratory specimens for 3 months after illness onset and persistent positive antigen tests are possible for at least 24 days. Replication-competent virus has not been reliably recovered from such patients, and they are not likely infectious.

Antigen testing of asymptomatic close contacts is recommended to identify a new infection if 31-90 days have passed since their first positive test. This is because persistent antigen positivity is unlikely after a month and because the probability of SARS-CoV-2 reinfection increases with time due to exposure to viral variants and waning immunity.

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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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