Coronavirus Disease 2019 (COVID-19)

• Reporting criteria
• The disease and its epidemiology
• Case definition

• Laboratory testing
• Case investigation

• Disease control measures
• References

What and how to report to the Colorado Department of Public Health and Environment (CDPHE) or local public health agency

• Positive SARS-CoV-2 laboratory results that can be reported via electronic laboratory reporting (ELR), COVID-19-associated hospitalizations, and deaths due to COVID-19 are each reportable within four (4) calendar days from specimen collection date, hospital admission date, or date of death, as applicable. Individual cases of COVID-19 are not reportable in Colorado.
• Outbreaks of all types and in all settings are reportable in Colorado. CDPHE prioritizes investigation of known or suspected outbreaks of COVID-19 in residential care facilities and in correctional settings. Suspected or confirmed outbreaks should be reported when there are:
  • Two or more residents with a positive COVID-19 test result occurring within a seven-day period, or
  • At least one resident with a positive COVID-19 test result and at least one resident with onset of undiagnosed respiratory illness occurring within a seven-day period, or
  • Three or more residents with onset of undiagnosed respiratory illness occurring within a three-day period

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Etiologic agent

COVID-19 is the disease caused by the 2019 novel coronavirus, SARS-CoV-2. SARS-CoV-2 was first identified in Wuhan, China, in December 2019 and rapidly spread throughout the world, inciting the most significant global pandemic since 1918. Coronaviruses are a large family of viruses that are common in humans and many different species of animals, including camels, cattle, cats, and bats. SARS-CoV-2 is a betacoronavirus (like SARS-CoV, the pathogen that causes SARS [severe acute respiratory syndrome], and MERS-CoV, the pathogen that causes MERS [Middle East respiratory syndrome]). Betacoronaviruses can cause more severe disease than other coronaviruses commonly circulating in humans if they jump from their animal reservoirs into human hosts. 

Clinical description

Infection with SARS-CoV-2 causes a broad spectrum of illness. A meta analysis published in 2021 estimates up to 40% of cases are asymptomatic. However, the proportion of asymptomatic cases varies based on age, the circulating variant, and the vaccination coverage in a given population. Symptoms of COVID-19 may include olfactory dysfunction, cough, shortness of breath, fever, altered mental status, chills, myalgia, fatigue, congestion, rigors, headache, sore throat, nausea/vomiting, or diarrhea. Illness can be severe, requiring hospital admission and the need for mechanical ventilation. Severe illness can include acute respiratory distress syndrome (ARDS) or other respiratory failure, septic shock, other organ system failure, or death. The severity of COVID-19 disease is associated with a number of factors, including, but not limited to, age, presence of underlying comorbidities, the circulating variant, and vaccination status. 

Long COVID is a chronic condition that persists for three or more months after the primary infection with SARS-CoV-2. Persistent symptoms may include difficulty breathing/shortness of breath, fatigue, sleep problems, brain fog, long-term olfactory dysfunction, post-exertional malaise, and more. Ongoing research continues to characterize the burden of post-COVID conditions and identify ways to prevent Long COVID.

Multisystem inflammatory syndrome in children (MIS-C) is a severe delayed hyperinflammatory condition in children and adolescents (< 21 years of age) occurring two to six weeks after a SARS-CoV-2 infection (the virus that causes COVID-19). MIS-C is a reportable condition in Colorado. For information about MIS-C, visit the MIS-C chapter in the CDPHE Communicable Disease Manual.

Reservoirs

SARS-CoV-2 is a betacoronavirus with a zoonotic origin, but the original reservoir has yet to be identified. Bats are suspected to be the natural reservoir, with possible intermediate hosts, including palm civets, pangolins, and other animals present in Wuhan wildlife markets. SARS-CoV, the virus that causes SARS, took 15 years from onset of the first case until the natural reservoir (horseshoe bats) was verified. In addition to humans, SARS-CoV-2 can infect several different animals, including cats (large and domestic), otters, mink, deer, and non-human primates. It is unclear which, if any, of these animals can transmit the virus (to humans or other animals) when infected and which serve as dead-end hosts. 

Modes of transmission

The SARS-CoV-2 virus is transmitted person to person, primarily through short-range aerosols and respiratory droplets. Fomite transmission, or transmission through contaminated objects or surfaces, is considered a possible but less likely route of transmission. Transmission occurs when a susceptible individual breathes in aerosolized droplets that an infected individual has exhaled or comes into direct contact with secretions from the respiratory tract of an infectious individual. There is a likely dose-response relationship between the magnitude of exposure and the likelihood of infection. An infectious individual singing, coughing, or loudly talking may expel more virions into the air and increase the risk of onward transmission. The number of virions needed to infect a human host is unknown and likely depends on host characteristics. Ventilation, vaccine status, usage of face coverings or respirators, distance from the infectious individual, and time spent with the infectious individual are all important factors that affect SARS-CoV-2 transmission dynamics. Variants of concern, such as the delta and omicron variants, may contain mutations that confer fitness advantages and allow transmission to occur more rapidly and efficiently than with the original SARS-CoV-2 lineage or other previously identified variants.

Incubation period

The incubation period ranges from two to 14 days from exposure to symptom onset, with an estimated mean of two to four days for omicron variants. Some variants may have a shorter incubation period.

Infectious period

The infectious period for SARS-CoV-2 ranges from two days before symptom onset to 10 days after symptom onset. Infected people who are asymptomatic can also transmit the virus. For symptomatic individuals, peak infectivity occurs immediately prior to onset of symptoms to shortly after symptom onset. Individuals who test positive for SARS-CoV-2 but never develop symptoms are considered to be infectious from two days before the positive collection date to 10 days after the positive collection date. Severely immunocompromised individuals may take 20 days (or even longer) after symptom onset or a positive test to completely clear infectious virus. Molecular testing is generally not recommended for 90 days following a positive test because remnants of viral RNA can remain in the nasal cavity, even if the individual is no longer infectious. However, reinfections can occur within the 90-day period. If symptoms develop within the 90-day period or an individual is asymptomatic but otherwise recommended to test between 30 and 90 days, antigen testing is recommended over NAAT testing.  

Epidemiology

Colorado detected its first two cases of COVID-19 on March 5, 2020. Both of these initial cases were likely exposed outside of Colorado, but within weeks, transmission within Colorado was confirmed.

Information about current transmission in Colorado is updated weekly on the CDPHE viral respiratory diseases dashboard. 

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Beginning in January 2025, individual cases of COVID-19 are not reportable in Colorado. However, positive laboratory results that can be reported via electronic laboratory reporting (ELR), COVID-19-associated hospitalizations, and deaths due to COVID-19 are reportable.

The case definitions that Colorado uses for COVID-19-associated hospitalization and death are derived from CSTE position statements and briefs, as well as CDC Emerging Infections Program (EIP) case definitions. There are currently no national case definitions for either condition. However, there is now a CSTE definition for COVID-19-associated pediatric mortality. CDPHE will perform chart review on suspected pediatric deaths and will transmit the case report form to CDC, as appropriate.

Positive COVID-19 lab

• Any positive, reportable COVID-19 lab test is captured in EpiTrax, Colorado’s Communicable Disease surveillance system, as a Confidential Morbidity Report (CMR). This includes detection of SARS-CoV-2 from a diagnostic molecular test (e.g., NAAT), by genomic sequencing, by diagnostic immunocytochemistry staining, or by antigen testing performed by a CLIA-certified provider. Serologic tests and home antigen tests are not reportable.
• Positive COVID-19 labs should only be reported when the testing lab uses ELR. CDPHE does not tabulate or report on the number of positive COVID-19 labs.
• The state case status in EpiTrax is marked “pending.” 

COVID-19-associated hospitalization 

• A person admitted to the hospital with a positive COVID-19 test during their hospitalization or within the 14 days prior to admission is considered a COVID-19-associated hospitalization. This includes patients tested at their primary care provider’s office, an urgent care facility, a long-term care facility, or an emergency room before being hospitalized.
  • ER visits are not hospitalizations.
  • Patients admitted for observation > 24 hours are considered hospitalized.
  • Positive COVID-19 tests include nucleic acid amplification or antigen tests performed by a CLIA-certified provider. Serologic tests and home antigen tests are not used to define a COVID-19 associated hospitalization.
  • Hospitalization outside of the 14-day time period after their first positive test should also be reported if it is determined that the hospitalization was related to their infection. This includes positive tests at any time during a hospitalization per EIP protocol.
• The state case status in EpiTrax for any person meeting the COVID-19-associated hospitalization definition is “confirmed.” 

Death due to COVID-19

• A person for whom a death certificate indicates COVID-19 or an equivalent term as an immediate, underlying, or contributing cause of death, or a case investigation determines COVID-19 was a cause of death and,
• The death occurred up to one year after a COVID-19 infection based on the collection date of the first positive test.
• If there is no laboratory test, the onset date is used. If the onset date is unknown, the report to public health date is used.
• The state case status in EpiTrax for any person meeting the death due to COVID-19 definition is “confirmed.” 

Outbreak definitions for special settings

Residential care facilities

Residential care facilities include skilled nursing facilities, assisted living residences, intermediate care facilities, and group homes for individuals with intellectual or developmental disabilities licensed or certified by CDPHE.

Confirmed COVID-19 outbreak in a residential care facility: 

• Two or more residents with a positive COVID-19 test result occurring within a seven-day period

Suspected COVID-19 outbreak in a residential care facility:

• At least one resident with a positive COVID-19 test result and at least one resident with onset of undiagnosed respiratory illness occurring within a seven-day period or
• Three or more residents with onset of undiagnosed respiratory illness occurring within a three-day period

Correctional settings

Correctional settings include state prisons, county and city jails, community corrections, detention settings, and work release facilities.

Confirmed COVID-19 outbreak in a correctional setting: 

• Two or more residents with a positive COVID-19 test result occurring within a seven-day period

Suspected COVID-19 outbreak in a correctional setting: 

• At least one resident with a positive COVID-19 test result and at least one resident with onset of undiagnosed respiratory illness occurring within a seven-day period

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A person who is symptomatic should be tested for both SARS-CoV-2 and influenza, or follow-up testing should be done for influenza if the SARS-CoV-2 test result is negative. In congregate settings, such as residential care facilities or correctional settings, it is important to test for other respiratory pathogens to determine potential co-infection or outbreaks of other respiratory illnesses (i.e., RSV). It is possible for co-infection with influenza and SARS-CoV-2 to occur. Therefore, testing is the best method to inform proper infection control and clinical management. If there are simultaneous outbreaks of COVID-19 and influenza, test continuously to confirm whether anyone with influenza-like illness is positive for COVID-19, influenza, or both. Further information about laboratory testing in Colorado is available online. 

State Laboratory services

The Colorado State Public Health Laboratory can perform COVID-19 testing on a limited basis in unusual situations with approval from the Communicable Disease Branch. More information is available on CDPHE’s laboratory services webpage. 

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CDPHE does not recommend routine investigation of positive SARS-CoV-2 labs, COVID-19-associated-hospitalizations, or deaths due to COVID-19, unless there is a concern for an outbreak in a residential care facility, correctional setting, or other priority setting. 

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Certain health behaviors can help prevent becoming ill with or spreading the COVID-19 virus. Taking precautions such as washing hands often, avoiding contact with people who are ill or limiting contact if personally ill, covering coughs and sneezes, avoiding touching eyes, nose, and mouth, and cleaning/disinfecting surfaces can reduce spread of COVID-19. Someone who may be sick with a respiratory virus should stay home and away from others. They can return to normal activities when, for at least 24 hours, their symptoms are getting better overall and they have not had a fever (and are not using fever-reducing medications). After they return to normal activities, they should take added precautions for the next five days such as steps for cleaner air, hygiene, masks, physical distancing, and/or testing when they will be around people indoors.

Current guidance for mitigating transmission of SARS-CoV-2 in different settings can be found on the CDPHE COVID-19 webpage under resources for businesses and organizations and resources for health care providers and local public health. 

For disease control during COVID-19 outbreaks, refer to the COVID-19 resources for long-term and residential care facilities. 

Vaccine

The COVID-19 vaccine helps protect against severe illness, hospitalization, and death. For current information about COVID-19 vaccines, see the CDPHE COVID-19 vaccine webpage.

Treatment

For current information about therapeutics available for treatment and prophylaxis, as well as eligibility and availability, see the CDPHE COVID-19 treatments webpage.

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CSTE: Revised COVID-19-associated Death Classification Guidance for Public Health Surveillance Programs. Available from URL: https://preparedness.cste.org/wp-content/uploads/2022/12/CSTE-Revised-Classification-of-COVID-19-associated-Deaths.Final_.11.22.22.pdf

CSTE: Interim Guidance for Public Health Surveillance Programs for Incident Case Classification of COVID-19-associated Hospitalizations. Available form URL: https://preparedness.cste.org/wp-content/uploads/2022/10/Interim-CSTE-Guidance-for-COVID-Hospitalization.pdf

CDC: COVID-19 Surveillance After Expiration of the Public Health Emergency Declaration – United State, May 11, 2023. Available from URL: https://www.cdc.gov/mmwr/volumes/72/wr/mm7219e1.htm?s_cid=mm7219e1_w

CDC: COVID Clinical Care Reference Guide. Available from URL: https://www.cdc.gov/covid/hcp/clinical-care/index.html

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