H9N2 is a LPAI (low path avian influenza) virus that is ubiquitous in Asian and Middle Eastern poultry, and while it generally causes little harm to birds, has been linked to the reassortment and evolution of far more dangerous avian flu viruses.
Its internal genes can be found in such novel and dangerous flu viruses as H5N1, H5N6, and H7N9.
H9N2 infections in humans - while rarely reported - are almost certainly more common than we know, primarily because surveillance in humans is very limited in the regions where it circulates.
A 2014 seroprevalence study, however, found antibodies against H9N2 ranged from 5.9% to 7.5% among poultry exposed individuals in Egypt.
On the positive side, H9N2 infection in humans has generally been mild, and no human-to-human spread has been detected. It is viewed as having some pandemic potential, and so a several candidate vaccines have been developed over the years.
Last February, after an H9N2 case was reported from China, the WHO wrote:
A total of 28 laboratory-confirmed cases of human infection with avian influenza A(H9N2) viruses, none fatal, have been detected globally. In most human cases, the associated disease symptoms have been mild and there has been no evidence of human-to-human transmission. Influenza A(H9N2) viruses are enzootic in poultry populations in parts of Africa, Asia and the Middle East. The majority of viruses that have been sequenced belong to the A/quail/Hong Kong/G1/97 (G1), A/chicken/Beijing/1/94 (Y280/G9), or Eurasian clades.
The most complete list of H9N2 we have online can be found at FluTrackers Global Cumulative H9N2 Partial Case List 1998-2016 and the last case we saw reported came from Egypt in May.
Overnight several Chinese language media outlets have carried reports of a 4 y.o. girl admitted to a Guangdong hospital in serious condition with the H9N2 virus.
This one (h/t Sharon Sanders of FluTrackers) is from the China News Network. So far, I've not found any official announcement on the government websites.
Meizhou City, Guangdong reported a case of H9N2 cases
Source: China News Network
Original title: Meizhou City in Guangdong reported a case of H9N2 cases
BEIJING, Guangzhou, June 18 (by Cai Minjie) Health and Family Planning Commission of Guangdong Province briefing on the 18th night, Meizhou case report H9N2 cases, present the case patients sicker.
According to the briefing, the patient Luo, female, 4 years old, now living in Meizhou Xingning City. June 18 confirmed H9N2 cases, patients present serious condition in Meizhou City hospitals admitted in hospital.
Guangdong CDC experts believe, H9N2 virus is a subtype of influenza A virus, the source of the virus is poultry in bird flu more common for people is a low pathogenic virus. The case of human infection with H9N2 found in sporadic cases belong to lower the risk of virus transmission.
Guangdong CDC experts have warned that the public should remain vigilant, as far as possible to avoid live bird markets, not to buy products of unknown origin of birds.