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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
  • Fully 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:

    The signs and symptoms present at illness onset of COVID-19 vary, but over the course of the disease, most patients with confirmed COVID-19 have developed an influenza-like illness with fever and lower respiratory tract symptoms. Atypical presentations often occur and older adults and person with medical co-morbidities may have delayed presentation of fever and respiratory symptoms. Asymptomatic infections have been well documented as well.

    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

    Various other symptoms have been associated with COVID-19, see CDC Interim Clinical Guidance for Management of Patients with Confirmed Coronavirus Disease for a more detailed discussion of COVID-19 presentations in adults. Signs and symptoms of COVID-19 in children vary by age of the child, and are usually milder compared to adults. For more information on the clinical presentation and course among children, see Information for Pediatric Healthcare Providers.

    NOTE: Clinical presentation among reported cases of COVID-19 varies in severity from asymptomatic infection to mild illness to severe or fatal illness. Some reports suggest the potential for clinical deterioration during the second week of illness.

  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:
    Probable case
    -from CSTE (to be used in outbreak settings and for close contacts)

In the absence of a more likely diagnosis:

  • At least TWO of the following symptoms:
    • Fever (measured or subjective)
    • Chills
    • Rigors
    • Myalgia
    • Headache
    • Sore Throat
    • Nausea or vomiting
    • Diarrhea
    • Fatigue
    • Congestion or runny nose


  • Any ONE of the following symptoms:
    • Cough
    • Shortness of breath
    • Difficulty breathing
    • New olfactory disorder
    • New taste disorder


  • Severe respiratory illness with at least one of the following:
    • Clinical or radiographic evidence of pneumonia
    • Acute respiratory distress syndrome (ARDS)

        Confirmatory laboratory evidence:
  • Detection of SARS-CoV-2 RNA in a clinical or autopsy specimen using molecular amplification test (e.g. reverse transcriptase-polymerase chain reaction [RT-PCR]).

        Presumptive laboratory evidence:
  • Detection of SARS-CoV-2 by rapid antigen test in a respiratory specimen.

        Supportive laboratory evidence:
  • Detection of specific antigen by immunocytochemistry in an autopsy specimen
  • Detection of specific antibody in serum, plasma, or whole blood.


2-14 days; average 4 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.

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

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

Communicability/Period of Infectiousness

Available data indicate that persons with mild to moderate COVID-19 remain infectious no longer than 10 days after symptom onset. Most adults with more severe to critical illness or severe immunocompromise likely remain infectious no longer than 20 days after symptom onset. There have been several reports, however, of persons with severe immunocompromise shedding replication competent virus beyond 20 days. See CDC Decision Memo.

The current period of infectiousness of a case begins 2 days before symptom onset and continues until both the following conditions are met:
  •  At least 10* days have passed since symptoms first appeared and
  •  At least 24 hours have passed since last fever without the use of fever-reducing medications and
  •  Symptoms have improved (e.g., cough, shortness of breath).

Asymptomatic persons with laboratory confirmed COVID-19 are considered infectious from 2 days before the date of their first positive molecular test (e.g. PCR) until at least 10 days* after the initial positive PCR test, barring the development of symptoms.

*For patients with severe to critical illness, the CDC recommends extending the duration of isolation or precautions from 10 days to up to 20 days from illness onset.

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.

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).

Determining Close Contacts

A close contact is a person with exposure to a confirmed or suspected 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.

Exposures are generally defined as:

  1. An individual who was within 6 feet of the case for a total of 15 minutes or more within a 24-hour period.
  2. An individual who had unprotected contact with the case’s body fluids and/or secretions, for example, being coughed or sneezed on, sharing utensils or saliva, or providing care without wearing appropriate protective equipment.

A person is still considered exposed even if the case or the contact was wearing a face covering.

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.

See site specific B73 for more specific guidance on determining close contacts. For more information see CDC Public Health Guidance for Community-Related Exposure.

Specific Treatment

Supportive care (e.g., rest, antipyretics, fluids, etc.). Patients with a mild clinical presentation may not initially require hospitalization. However, clinical signs and symptoms may worsen with progression to lower respiratory tract disease; all patients should be monitored closely.

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.


Natural immunity: The duration and robustness of immunity to SARS-CoV-2 remains under investigation. Among other human coronaviruses, reinfection appears to occur variably over time after onset of infection. SARS-CoV-2 reinfection appears to be uncommon during the initial 90 days after symptom onset of the preceding infection. The likelihood of re-infection is expected to increase over time because of waning immunity and the possibility of exposure to virus variants. See CDC Interim Guidance on Ending Isolation and Precautions for Adults with COVID-19.

Vaccine-induced immunity: Currently authorized vaccines in the United States are highly effective at protecting vaccinated people against symptomatic and severe COVID-19. Fully vaccinated people are less likely to become infected and, if infected, to develop symptoms of COVID-19. Per the CDC, there is preliminary evidence that suggests that fully vaccinated people who do become infected with the Delta variant can be infectious and can spread the virus to others.

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 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 and some molecular 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

Fully Vaccinated Persons

A person is considered fully vaccinated ≥2 weeks following the receipt of:

  • the second dose in a 2-dose series (Pfizer-BioNTech or Moderna)
  • one dose of a single-dose vaccine (Johnson and Johnson/Janssen).

* This guidance can also be applied to COVID-19 vaccines that have been listed for emergency use by the World Health Organization (e.g., AstraZeneca/Oxford).

Fully vaccinated persons who are a close contact to a confirmed COVID-19 case:

  • Do not need to quarantine as long as they are asymptomatic.
  • Should be tested after exposure.
  • Should be instructed to monitor their health for 14 days after the last contact with the infected person. If they develop symptoms consistent with possible COVID-19, they should be instructed to self-isolate pending clinical evaluation and SARS-CoV-2 testing. 

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
    • Retesting is not recommended.
    • They do not have to quarantine if exposed as a close contact.
    • They do not have to re-isolate for a repeat positive test.
    • 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 current 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.
*Lab confirmed=positive molecular or antigen test for SARS-CoV-2.

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