Table 1.
Comparisons of clinical and epidemiological features among AI infections in humans
| A(H5N1)8, 9 | A(H7N9)6, 10, 11, 12 | A(H5N6)13, 14, 15 | A(H9N2)16, 17, 18 | A(H10N8)19, 20 | A(H3N2)v21, 22, 23 | |
|---|---|---|---|---|---|---|
| Pathogenicity | HPAI | LPAI/HPAI | HPAI | LPAI | LPAI | N/A |
| First human case | Hong Kong in 1997 | China in 2013 | China in 2014 | Hong Kong in 1999 | China in 2013 | United States in 2011 |
| Regions with human cases | China, Laos, Cambodia, Thailand, Vietnam, Indonesia, Pakistan, Azerbaijan, Bangladesh, Turkey, Nigeria and Egypt | China, Taiwan, Malaysia and Hong Kong | China | Hong Kong, China, Bangladesh, serological evidence in Asia, Africa and Middle East | China | United States |
| Total number of human cases (years) | 903 cases (1997–2015) | 1625 cases (2013–2018)2 | 17 cases (2014–2016) | 28 cases (1999–2016) | 3 cases (2013–2014) | 405 cases (2011–2017) |
| Median ages (years) | 19 (5–32) | 61 (46–73) | 35 (26–45) in recent 9 cases reported by WHO | Mostly children | 73, 56, 75 |
7 (range, 3 months–74 years) <18 years in 92% |
| Onset of illness to hospitalization (days) | 4 (2–6) | 4 (3–6) | 3 (1–7) in recent 9 cases | N/A | 3, 7, 2 | 4 (1–16) in illness duration |
| Clinical characteristics |
Less URT symptoms Admission rate: 90.3% Advanced life supports: 63% |
ARDS: 57.8% MV: 61.5% |
Usually severe infections | Mild or asymptomatic illness | Bilateral severe pneumonia in all cases | Mild illness |
| Mortality rate | 53.3% | 38.3% | 58.8% | 0% | 66.6% | 1/405 |
| Epidemiological features |
67.2% between December and April Recent epidemic in Egypt (2014) |
Five epidemics Currently the largest epidemic |
Sporadic infections | Sporadic infections | Sporadic infections |
Sporadic infections A large epidemic in 2012 (n = 306) |
| Risk factors | Exposure to sick and dead poultry, and live poultry market | Exposure to live poultry (81.6%) | Exposure to dead poultry and live poultry | Exposure to live poultry and poultry farm | Exposure to live poultry market | Exposure to pigs |
†
Thirty‐two cases with HPAI A(H7N9) were recently reported.24
A(H3N2)v, A(H3N2) variant; AI, avian influenza; ARDS, acute respiratory distress syndrome; HPAI, highly pathogenic AI; LPAI, low pathogenic AI; MV, mechanical ventilation; N/A, not applicable; URT, upper respiratory tract; WHO, World Health Organization.