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B73 COVID-19

Home Page and Core Information
Procedural Guidance for DPH Staff

COVID-19 – Core Information

  • Agent, Identification, and Differential Diagnosis sections
  • Incubation, Reservoirs, Source, and Transmission sections
  • Communicability section
  • Specific Treatment and Immunity sections
  • Vaccinated Persons section
  • Diagnostic Procedures section
  • Testing of Patients with a History of Recent Recovery from COVID-19 section
  • Control Measures for Outbreaks section

B73 COVID Chapters


COVID-19 is caused by SARS-CoV-2, a human coronavirus first identified in December 2019. SARS-Cov-2 is an RNA virus and as a result it acquires mutations quickly. Often, new mutations occur that have no impact or may be detrimental to the virus. Occasionally, these mutations result in a competitive advantage against other versions (lineages) of the virus that are circulating. When this occurs, that lineage may become more prevalent in the population. If one of these lineages or groups of lineages have characteristics that impact public health (increases in severity, transmissibility, or evasion of existing immunity; resistance to therapeutics), those lineages may be considered a variant of concern or interest. 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-CoV-2 infection can experience a range of clinical manifestations, from no symptoms to critical illness. Age is the strongest risk factor for severe COVID-19 outcomes, with risk of severe outcomes increasing with advancing age. 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 or chills
    • Cough
    • Shortness of breath or difficulty breathing
    • Fatigue
    • Muscle or body aches
    • Headaches
    • New loss of taste or smell (less common with newer variants)
    • Sore throat
    • Congestion or runny nose
    • Nausea or vomiting
    • Diarrhea

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

    See the ISDA Real Time Learning Network 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, other human coronaviruses, Streptococcus pneumoniae, Legionella species, mycoplasma, and other atypical pneumonia agents.

Case Classification

Outbreak case classification may differ by sector. Please refer to setting-specific B73 chapters for further information about case classification.


The median time to symptom onset has decreased since SARS-CoV-2 initially emerged in late 2019. Newer lineages have a median incubation period of about 2-5 days.




Nasal and pharyngeal secretions.


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.

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


People with SARS-CoV-2 infection are likely most infectious in the first 5 days of illness. Most otherwise healthy individuals will have stopped shedding the virus by the 10th day after symptom onset.

Isolation duration and requirements for COVID-19 cases and close contacts vary by setting. See setting-specific B73 chapters for details.

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/.


Infection and vaccination provide limited protection against symptomatic illness that wanes over time. Reinfection is expected. Vaccination provides protection against severe illness, hospitalization and death.

Vaccinated Persons

Refer to the CDC Guidelines to determine when a person is considered up to date with their COVID-19 vaccines. Staying up to date is safe and important for everyone because it can increase prior protection (from previous vaccination or infection) that may have decreased over time. For local resources including information on where the vaccine is available visit VaccinateLACounty.com.

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 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.

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

Testing of 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 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.

Control Measures for Outbreaks

See the appropriate B73 chapters for setting-specific control measures, including control of cases and contacts.

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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