SEIR-DIT is a mathematical compartmental model aimed to study the effect of detection of symptoms, isolation and contacts tracing as an alternative to COVID-19 control.
The model is composed of two main ODE systems. A SEIR-like model (see Figure 1) that describes the epidemic dynamics and contains the main epidemiological states, and a secondary compartmental model (see Figures 2,3 and 4), fed by the main SEIR-like model, that allows to calculate the testing requirements and the amount of isolated cases and contacts at every time.
- S: Susceptible
- QS1: Quarantine for suspected index cases and contacts
- QS2: Quarantine for non-exposed traced contacts of detected mild infections
- E: Exposed
- ET: Exposed traced contacts of detected mild infections
- IM: Mild infections
- IMD: Detected mild infections
- IMT: Traced mild infections (coming from exposed traced contacts)
- IC: Infections requiring hospitalization
- ICSI: Self-isolated infections requiring hospitalization
- ICT: Traced infections requiring hospitalization (coming from exposed traced contacts)
- IHR: Hospitalized infections that require a general hospital bed and recover
- IUR: Hospitalized infections that require an ICU bed and recover
- IHD: Hospitalized infections that require a general hospital bed and die
- IUD: Hospitalized infections that requiring an ICU bed and die
- IR: Hospitalized infections requiring a general hospital bed after recovering from ICU stay
- R: Recovered
- D: Dead
Fig. 1. SEIR-like model |
- QIMD1: Detected mild infections with positive antigen test
- QS1: Quarantine for suspected index cases and contacts
- QS2: Quarantine for non-exposed traced contacts of detected mild infections
- QET: Exposed traced contacts (isolated after tracing)
- QIMT: Isolated mild infections (coming from traced exposed contacts)
- QIMT1: Traced mild infections with positive RT-PCR test
- QICT: Isolated infections requiring hospitalization (coming from traced exposed contacts)
Fig. 2. Isolation and testing of probable index cases | Fig. 3. Isolation and testing of suspected index cases and their contacts |
Fig. 4. Isolation and testing of exposed contacts |
Fig. 5. Isolation and testing of non-exposed contacts |
The parameters of the main SEIR-like model were adapted from https://mrc-ide.github.io/global-lmic-reports/parameters.html, assuming that the probability of death for critical cases is 0.35
Parameter | Value | Definition |
---|---|---|
R0 | 3.0 | Reproduction number |
β0 | 1.3743 | Transmission rate in absence of social distancing |
β1 | 0.0199 | Transmission rate within households |
b | - | Probability of transmitting the disease b=βM/n |
n | 15.721 | Average number of contacts per individual |
βH | 0.001 | Hospital transmission rate |
ω-1 | 4.6 days | Mean incubation period |
σC-1 | 3 days | Mean time upon self-isolation for severe infections |
σCSI-1 | 4.1 days | Mean duration of isolation for severe infections prior hospitalization |
σCT-1 | 7.1 days | Mean duration of isolation for traced contacts with severe infection prior hospitalization |
γM-1 | 2.1 days | Mean duration of mild infection |
γHR-1 | 9 days | Mean duration of hospitalization for non-critical cases if survive |
ν-1 | 14.8 days | Mean duration in ICU if survive |
γR-1 | 3 days | Mean duration of stepdown post ICU |
σHD-1 | 9 days | Mean duration of hospitalization for non-critical cases if die |
σUD-1 | 11.1 days | Mean duration in ICU if die |
δM | 0.97902 | Probability of mild infection |
δHR | 0.67959 | Probability of recovery for hospitalized infections requiring a general hospital bed |
δUR | 0.13883 | Probability of recovery for hospitalized infections requiring an ICU bed |
δHD | 0.10682 | Probability of dying for hospitalized infections requiring a general hospital bed |
δUD | 0.07476 | Probability of dying for hospitalized infections requiring an ICU bed |
Parameter | Value | Definition |
---|---|---|
α-1 | 1 day | Mean time between onset of symptoms and detection |
ρ-1 | 12 days | Mean duration of isolation period |
TPCR | 2 days | Mean time to results of RT-PCR test |
ξPCR | 0.85 | Sensitivity of RT-PCR test |
TAG | 1 days | Mean time to results of AG test |
ξAG | 0.75 | Sensitivity of AG test |