Continuing its steady trickle of H7N9 cases, China reported three more today, as new research findings implicated chickens as the main source of the virus and emphasized the importance oropharyngeal swabs for testing birds.
Human cases in the outbreak's second wave continue to taper, with sporadic cases mainly reported from recent hot spots, as well as other provinces that reported earlier cases.
New cases in Hunan, Jiangsu provinces
Two of the new case-patients are from Hunan province, a 77-year-old man and a 41-year-old man who are hospitalized, according to a provincial health department statement translated and posted by FluTrackers, an infectious disease news message board.
The third case-patient is from Jiangsu province, a 42-year-old man who apparently bought chickens at a local market and is hospitalized in serious condition, according to a provincial notice flagged by FluTrackers.
Today's new cases boost the overall outbreak total to 376 infections, with the number of deaths holding steady at 114. So far 240 H7N9 illnesses have been confirmed in the second wave that's currently under way, compared with 136 recorded last spring during the first wave.
In a related development, the World Health Organization (WHO) today provided details on five more case notifications it received from China on Feb 23 and Feb 24, all from Guangdong province. Three are in men, and patient ages range from 31 to 76.
Four of the five patients had been exposed to live poultry before they got sick. Illness-onset dates range from Feb 16 to Feb 19. Four of them are hospitalized in critical condition, while one is listed in stable condition.
Poultry tests find high shedding in quail, chickens
Meanwhile, experiments that involved infecting different poultry species with H7N9 conducted at the US Department of Agriculture (USDA) Southeast Poultry Research Laboratory (SEPRL) in Athens yielded new clues about likely reservoirs and promising testing methods.
The group published its findings yesterday in the latest online issue of the Journal of Virology.
Many human cases had involved live poultry or their environments, and health officials have suspected that poultry infected with low-pathogenic viruses, which typically infect birds without causing symptoms, are the main drivers of the outbreak.
Agriculture officials in China have tested thousands of birds, and have found H7N9 in only a small number of them. These have included chickens, plus a small number of pigeons and ducks. Also, a recent report from Chinese researchers described the isolation of H7N9 from an apparently health tree sparrow collected last spring in Shanghai.
To get a better handle on which species are most likely to be infected and shed enough virus to infect humans, the SEPRL intranasally inoculated chickens, Japanese quail, pigeons, Pekin ducks, mallard ducks, Muscovy ducks, and Emden geese with H7N9 virus. The birds became infected but showed no clinical signs.
Quail and chickens shed the virus at much higher levels and for longer times than other birds. The team found that quail transmitted the virus to their direct contacts, but pigeons and Pekin ducks didn't.
For all of the species, researchers recovered the virus at much higher levels from oropharyngeal swabs than from cloacal swabs.
Researchers said that the findings show that quail and chickens probably play an important role in spreading the virus to humans.
Study suggests longer incubation period
In other developments, researchers from China looked back at 27 human H7N9 cases detected in Jiangsu province to get a better idea of the incubation period for the disease. Their report appeared online Feb 24 in Epidemiology and Infection.
The incubation period for H7N9 is generally thought to be 3 to 7 days, but it has been reported to be as long as 10 days. The US Centers for Disease Control and Prevention, for example, recommends that close contacts of H7N9 case-patients be monitored for 10 days after their last known exposure.
A detailed look at patients' poultry exposures and infection onsets found that the median incubation period was 6 days with a single known exposure (range 2 to 10 days) and 7.5 days when patients were exposed on multiple days (range, 6.5 to 12.5 days). Taken together, the overall median incubation period was 7.5 days.
The group noted that the findings suggest that health officials should extend the medical surveillance period from 7 days to 10 days.
Feb 27 FluTrackers thread
FluTrackers human H7N9 case count
Feb 27 WHO statement
Feb 26 J Virol abstract
Feb 24 Epidemiol Infect abstract