COVID-19: Epidemiology and pathophysiology

Virology

Coronaviruses are common human pathogens
- Cause the common cold
- In epidemics, cause up to one-third of community-acquired upper respiratory tract infections in adults; and may cause diarrhea in infants and children
SARS-CoV-2 is a novel coronavirus (a new strain not previously identified in humans)
- Likely primary source = bats
- It is a betacoronavirus in the same subgenus as the severe acute respiratory syndrome (SARS) virus. Middle East respiratory syndrome (MERS) virus is another, more distantly related, betacoronavirus. Like the SARS coronavirus, SARS-CoV-2 uses angiotensin-converting enzyme 2 [ACE2] for cell entry

ARDS - Possibly due to direct alveolar damage by the virus AND inflammatory reaction. ^[1]
Cytokine Storm

Disease Severity
- 80% have mild symptoms
- 15% have severe disease requiring hospitalisation
- 5% require mechanical ventilation

Risk Factors
- Older age
- Underlying conditions (lung disease, Renal Failure, Malignancy, heart disease, diabetes)

Ro Example

Reproduction Number (R0) SARS-CoV-2:
- R0 = 2.2 - 4.2
- Where R0 = expected number of secondary cases produced by a single typical infection in a susceptible population (basic reproductive rate)
- R0 for seasonal flu ~ 1.3
- R0 for pandemic flu ~ 1.5-1.8

Incubation Period:
- Incubation = 5 days (median); range of 2-14 days
- Serial interval duration = 7.5 days
  - Serial interval refers to the time from illness onset in successive cases in a transmission chain

Surface survival time of SARS-CoV-2:
- stainless steel: persists for 3 hours (or longer)
- underscores the importance of environmental cleaning / disinfection
- cleaning gets rid of the proteins that would interfere with a disinfectants effectiveness
  - Note: studied in a simulated lab environment. Lab virions not covered in protein and mucus and other things that would mimic real life and that could prolong survival

↑ Xu Z, Shi L, Wang Y et al. Pathological findings of COVID-19 associated with acute respiratory distress syndrome. The Lancet Respiratory Medicine. 2020;8(4):420-422. doi:10.1016/s2213-2600(20)30076-x

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