Susceptible (S) individuals
Individuals who are healthy, have never been previously infected with SARS-CoV-2, and have no antibodies to SARS-CoV-2.
Exposed (E) individuals
Individuals who have recently been exposed and infected with the virus. There are six stages of exposed individuals, E1 to E6. The duration of this exposed period or incubation period follows an Erlang distribution with coefficient of variation equal to 0.41. These individuals do not show symptoms. Individuals in stages E5 and E6 of the incubation period may be infectious.
Asymptomatic (A) individuals
Individuals who are past the incubation period and either (1) do not show any symptoms, or (2) have mild enough symptoms which under normal circumstances would not result in them reporting to a hospital or clinic. These individuals probably have a moderate to low viral loads in their lungs and URT. They are infected and may be shedding virus at low rates. As in other publications, these individuals’ transmissibility has been assumed to be half of the infectivity of an infected and symptomatic individual. There are four stages of asymptomatic infection, A1 to A4. The coefficient of variation of the asymptomatic period is 0.5.
Infected (I) individuals
These individuals are symptomatic and infected. Moving from E6 to I1 means that the individual developed symptoms. Infected individuals are not hospitalized. Their symptoms may be moderate or somewhat severe, but not severe enough to be admitted to a hospital. There may be individuals in the I-class who have dyspnea but no hypoxia and no other underlying conditions. Current (April 4) indication for patients with (1) dyspnea, (2) no hypoxia, (3) no additional underlying complications is to be treated as an outpatient.
Hospitalized (HA) individuals, acute-stage
These individuals are hospitalized on the medical floor level of care (not ICU). The acute-stage designation means that these patients recently arrived at the hospital and may be at risk for progressing to more sever symptoms and ICU admission. These individuals will likely have a nasal cannula attached, but will not have high-flow oxygen as a high-flow oxygen patients need to be isolated. These patients may or may not have hypoxia, and they may or may not have dyspnea. For the average non-lung-diseased patient, one would experience dyspnea first and hypoxia second.
- Dyspnea and hypoxia together mean that an individual will be hospitalized.
- Hospitalized patients may have no dyspnea, no hypoxia, but be admitted due to an underlying condition (e.g. kidney complications). These patients would receive non-invasive ventilation.
- Death is possible on the regular medical floor level of care. An older individual can destabilize quickly and die within hours before there is a chance to move the patient into the ICU. Whether this patient is moved into the ICU or not will often depend on a hospital’s guidelines and protocols, and whether beds in the ICU are available.
Critical Care (C) Patients, i.e. in the ICU, but not on a ventilator
This will include two types of patients (1) patients that need high-flow oxygen, and (2) patients that progressed to critical condition for other reasons. Individuals in the high-flow oxygen group may cause virus to aerosolize from within the nose and may be infectious to health care workers.
Patients on Ventilators (V), in the ICU necessarily
Often, patients are admitted to the ICU because they require mechanical ventilation. Individuals in this class can have ARDS, which implies that the mechanical ventilation is failing. This class does not include non-invasive mechanical ventilation.
Critical Care (CR) individuals, recovering stage
Patients in ICU, after they have come off a mechanical ventilator.
Hospitalized (HR) individuals, recovering stage
Patients in medical floor level of care, after they have been discharged from the ICU.
Recovered (R) individuals, recovering stage
Patients who survived infection, have no viral load, cannot transmit to anyone else, and are fully immune.
Recovered (RHOSP) individuals who have been discharged from a hospital (v5 only)
Patients who survived infection after hospitalization, have no viral load, cannot transmit to anyone else, and are fully immune.
Deceased (D) individuals
Deceased individuals. (In v5, this is deceased individuals who died at home or in their place of residence, e.g. an elderly care center)
Deceased (DHOSP) individuals who died in a hospital (v5 only)
Deceased individuals who died during hospitalization.