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This award-winning blog supplements the articles in Hospital Infection Control & Prevention.

Novel H7N9 influenza A cluster suggests human-to-human transmission

As novel influenza A virus (H7N9) continues to emerge in China there is a cluster suggesting human-to-human transmission may have occurred, an epidemiologist at the World Health Organization reports.

“We had one confirmation in the very sad case of the father and his two sons who were also ill,” Michael O’Leary, MD, MPH, WHO Representative in China, said at a recent press conference.

The father and the younger son died, and blood tests show that both the father and the older son had H7N9. That other son has now recovered from pneumonia, said O’Leary, a former Epidemic Intelligence Officer for the U.S.Centers for Disease Control and Prevention.

“This might be a case of one person passing the disease to another, or they may have all been exposed to the same source of infection,” he said. “I want to clarify that even though we are concerned if the disease can pass from one person to another, it still seems that this does not happen easily, or we would see many such cases. We have not seen easy and sustained person-to-person transmission. This is the situation for which we are most vigilant.”

There have been no cases in the U.S., but the CDC is advising clinicians to be alert for infections in patients with recent travel to China.

Flu viruses are nothing if not unpredictable, but O’Leary theorized if would take a “separate mutation” of the current H7N9 strain for it to become more easily transmittable between humans.

The continuing mystery is the full source of the virus, which is of avian appearance but seems to be coming from a reservoir beyond poultry. More than half the H7N9 human cases apparently had no contact with poultry, O’Leary said.

Poultry is certainly part of the reservoir of virus, but properly cooked chicken poses no danger of transmission, he emphasized.

“[Poultry] remains our strongest line of investigation because, first of all this is an avian related virus, and also [with] many — but not all of the cases — [we] have been able to demonstrate a link to poultry,” he said. “[What] is a bit unusual [is that] we haven’t been finding sick poultry effectively. The tests have been done as part of the investigation. There’s been more than 80,000 birds tested so far, with fewer than 40 positive and they were not sick. So that’s unlike some previous investigations [i.e., H5N1 avian flu] where this was a serious infection among the poultry population as well.”

As a “novel,” i.e., a “non-human” virus, H7N9 has the potential to cause a pandemic in a human population that is likely completely susceptible — if it acquires the capacity to easily transmit between people. H7N9 had never previously been demonstrated to infect any mammalian species.

For more this story see May 2013 issue of Hospital Infection Control & Prevention