Table 1. Characteristics of influenza A(H5N1) and A(H7N9) infection and implications for surveillance system detection of A(H7N9) in humans and animals*.
| Characteristic | A(H5N1) | A(H7N9) | Reference | Surveillance system implications for A(H7N9) detection |
|---|---|---|---|---|
| Clinical signs and symptoms |
Fever, cough, pneumonia, respiratory failure |
Fever, cough, pneumonia, respiratory failure |
(1,4) |
SARI and ILI surveillance systems should detect with equal efficacy |
| Disease severity |
Critical and fatal (60%) |
Most are critical; mild infections reported in children |
(4) |
Hospital-based platforms would be most likely to detect cases |
| Patient age, y |
<20 |
>60 |
(4) |
Surveillance systems that do not cover older adults may not detect case |
| Seasonality |
December–March (average) |
Most cases in 2nd wave occurred December–March 2013–2014 |
(3) |
Surveillance will be more likely to detect a case when the virus in circulating; however, additional data are needed to establish the seasonality of A(H7N9) |
| Geography |
Primarily rural (farm) |
Primarily urban (LBM) |
(4) |
Surveillance systems that do not cover visitors to LBMs may be unable to detect cases |
| Transmissibility from poultry or environment to humans |
Appears low |
Appears moderate |
(10) |
Surveillance systems should assess for poultry or environmental exposures, and known exposures should prompt testing in suspected cases of avian influenza |
| Person-to-person transmission |
Appears uncommon |
Appears uncommon |
(1,11) |
Surveillance systems will probably detect sporadic cases that have identifiable poultry exposures |
| History of poultry exposure |
Common |
Common |
(4) |
Animal surveillance is critical for detection in poultry and assisting with targeting control measures |
| Pathogenicity in chickens |
High |
Low |
(5,11) |
Infection with A(H7N9) does not appear to cause disease in poultry. Surveillance for detecting A(H7N9) in poultry requires targeted risk assessment and active testing. |
| Effects in wild bird species | Detected in wild bird species | Limited data | (11–13) | Poultry surveillance directed at either back-yard farms or commercial poultry farms (depending on prevalence) and LBMs should be sufficient to detect cases |
*ILI, influenza-like illness; LBM, live-bird market; SARI, severe acute respiratory infection.