The median incubation period for COVID-19 is 4 to 5 days; the range is 2 to 14 days (Figure 8.1).
Figure 8.1 Proportion of symptomatic cases per day since infection.
Studies suggest that illness severity can range from mild to critical (Table 8.1):
Table 8.1 Illness severity for COVID-19.
According to reports from China:
It is important to note that some patients rapidly deteriorate 1 week after illness onset.
Among patients who developed severe disease, the medium time to dyspnea ranged from 5 to 8 days; the median time to ARDS ranged from 8 to 12 days; and the median time to ICU admission ranged from 10 to 12 days, with 26% to 32% of patients admitted to the ICU. There have been different reports, but mortality among patients admitted to the ICU ranged from 39% to 72%. The median length of hospitalization among survivors was 10 to 13 days.
Development of ARDS was reported in:
Age is a strong risk factor for severe illness, complications, and death. According to CDC reports, among the 1,482 patients hospitalized with COVID-19, 74.5% were aged ≥50 years, and 54.4% were male. The hospitalization rate among patients identified through COVID-NET during this 4-week period was 4.6 per 100,000 population. Rates were highest (13.8) among adults aged ≥65 years (Figure 8.2).
Among more than 44,000 confirmed cases of COVID-19 in China, the case fatality rate was highest among older persons:
Patients in China with no reported underlying medical conditions had an overall case fatality of 0.9%, but case fatality was higher for patients with comorbidities:
Heart disease, hypertension, prior stroke, diabetes, chronic lung/respiratory disease, cancer , and chronic kidney/renal disease and obesity have all been associated with increased illness severity and adverse outcomes.
Figure 8.2 Laboratory-confirmed coronavirus disease 2019 (COVID-19)–associated hospitalization rates,* by age group — COVID-NET, 14 states,a March 1, 2020, to March 30, 2020 (Garg S, Kim L, Whitaker M, et al. Hospitalization rates and characteristics of patients hospitalized with laboratory-confirmed coronavirus disease 2019 — COVID-NET, 14 states, March 1-30, 2020. MMWR Morb Mortal Wkly Rep. 2020 Apr 17;69(15):458-464. doi:10.15585/mmwr.mm6915e3).
COVID-NET = Coronavirus Disease 2019–Associated Hospitalization Surveillance Network
* Number of patients hospitalized with COVID-19 per 100,000 population.
a Counties included in COVID-NET surveillance: California (Alameda, Contra Costa, and San Francisco counties); Colorado (Adams, Arapahoe, Denver, Douglas, and Jefferson counties); Connecticut (New Haven and Middlesex counties); Georgia (Clayton, Cobb, DeKalb, Douglas, Fulton, Gwinnett, Newton, and Rockdale counties); Iowa (one county represented); Maryland (Allegany, Anne Arundel, Baltimore, Baltimore City, Calvert, Caroline, Carroll, Cecil, Charles, Dorchester, Frederick, Garrett, Harford, Howard, Kent, Montgomery, Prince George’s, Queen Anne’s, St. Mary’s, Somerset, Talbot, Washington, Wicomico, and Worcester counties); Michigan (Clinton, Eaton, Genesee, Ingham, and Washtenaw counties); Minnesota (Anoka, Carver, Dakota, Hennepin, Ramsey, Scott, and Washington counties); New Mexico (Bernalillo, Chaves, Dona Ana, Grant, Luna, San Juan, and Santa Fe counties); New York (Albany, Columbia, Genesee, Greene, Livingston, Monroe, Montgomery, Ontario, Orleans, Rensselaer, Saratoga, Schenectady, Schoharie, Wayne, and Yates counties); Ohio (Delaware, Fairfield, Franklin, Hocking, Licking, Madison, Morrow, Perry, Pickaway and Union counties); Oregon (Clackamas, Multnomah, and Washington counties); Tennessee (Cheatham, Davidson, Dickson, Robertson, Rutherford, Sumner, Williamson, and Wilson counties); and Utah (Salt Lake County).
The hospitalization rate among children is shown in Figure 8.3.
Figure 8.3 COVID-19 cases among children* aged <18 years, among those with known hospitalization status (N = 745),a by age group and hospitalization status — United States, February 12, 2020, to April 2, 2020 (CDC COVID-19 Response Team. Coronavirus disease 2019 in children — United States, February 12-April 2, 2020. MMWR Morb Mortal Wkly Rep. 2020 Apr 10;69(14):422-426. doi:10.15585/mmwr.mm6914e4).
* Includes infants, children, and adolescents.
a Number of children missing hospitalization status by age group: <1 year (303 of 398; 76%); 1-4 years (189 of 291; 65%); 5-9 years (275 of 388; 71%); 10-14 years (466 of 682; 68%); and 15-17 years (594 of 813; 73%).