A case fatality rate can only be calculated for people where you know the outcome. At the time I wrote that, 9 people had died and one was considered recovered. That's 90%. You could have a million more people sick with it at the same time, but until you know whether they survive or recover, it doesn't factor into that statistic.

When I wrote my post yesterday, there were thirty-something cases reported, so if you're seeing 60 cases in the press today, that's almost a doubling in less than a day.

Early numbers on any influenza strain can be deceiving: they seldom separate out new detections versus finding past detections hidden in existing data. So 20% increases can be accounted for by newly discovered detections hidden in the data, and lethality figures are relative - most influenza As are known to carry human lethality potential, whether its proves to be 60% or 90% or some other number really remains to be seen.

Interesting new development--a 4-year old, symptom-less carrier has been found in Beijing.

The boy's neighbor bought chicken from the parents of the 7-year old girl, who is Beijing's first confirmed H7N9 case. The parents of the girl sell live chickens. Since the boy did not have direct contact with the chicken sellers or any chicken sold by the chicken sellers, it seems likely that he was infected through another person.

That could be good news, if it turns out that far more people than we currently know have actually gotten H7N9 and not even noticed it. Then it wouldn't be so lethal. In other words, it could mean H7N9 is far milder than initially thought.

Or, it could be bad news, if the virus is actually highly lethal and a small percentage of carriers allow the disease to spread undetected and unknowingly far and wide, person-to-person. The virus also doesn't seem to sicken birds much, if at all, which makes monitoring its spread in the bird population much more difficult.

Up to 63 cases now, last that I've read. That already exceeds the number of H5N1 cases ever seen in China over the course of a decade.

Its 90% of those hospitalized as I understand it.

It seems reasonable that only people who are really sick will be hospitalized.

Those who get mild cases may not even realize what they have.

Case fatality rate includes all known cases, whether hospitalized or not, but only cases where we know whether they recover or whether they die. You want an idea of how deadly a disease is overall, not just in the worst cases.

Think about it, if you had a million people infected and then got over some bug and only one elderly, frail person who became hospitalized and then died, the case fatality rate would be 100% if we only consider hospitalized people. That would seem misleading, doesn't it?

Now, where you'll find wiggle room in the definition is whether you only include laboratory confirmed cases or whether you go with a symptom-based one. In a fast developing epidemic, there are just too many cases to send to a lab, so you just use symptoms. So far, China seems to only be reporting laboratory confirmed cases to the press, and it seems like all cases are being hospitalized for now, even the 4-year old case who doesn't seem sick at all.

Up to 77 confirmed cases, last I read. Half or more of the cases (depending on who you ask) don't seem to have any direct connection to live poultry. So in my mind, either the disease vector is something else besides chickens, like pigeons, or else many of these people are catching it directly from another person.

The very limited number of genetic sequences released by the Chinese so far supports the theory that person-to-person transmission is already occuring in some cases. There are samples from infected people which share genetic markers that don't occur in any of the bird samples released so far. This suggests that the virus was acquired from another human rather than from a bird.

Last night I was reading a webpage (sorry, I closed the window and forgot where I found it) where a senior Chinese veterinarian (reporting under an alias) reported that authorities have been hiding a widespread poultry epidemic since last year. The area of the outbreak coincides with the areas where the inital human H7N9 cases appeared. In Shaanxi province IIRC, he mentions that the normal 20 million poutry population is down to 7 or 8 million (however, it's not clear if he means that they all died from the bird flu or if this figure includes flocks culled by the authorities and never reported in the media).

It sounds plausible to me. The mass cullings that have been going on periodically for more than a decade over bird flu fears have taken a heavy toll on poultry farmers and local economies. Locals want as little of it as possible since everyone loses out. Political advancement by local Chinese authorities often hinge on promoting good news and minimizing or hiding bad news in your area (well, this happens everywhere but it a particular problem in China). China is so spread out that Beijing often has little control over what happens on a day-to-day basis out in the provinces. A lot of what Beijing gets blamed for is decided at the local/regional level.

Anyway, so it's possible that the H7N9 virus has been around longer than the apparently sudden emergence in humans last month. It does raise interesting questions about whether people have been sick of it earlier, but was being mistaken for something else.

This is the only whiff of this story that I've seen anywhere, so I can't corroborate with any other sources.

Bloomberg is reporting that CDC has advised US hospitals to be on the lookout for possible H7N9 patients among people who have travelled to China recently and are exhibiting flu-like symptoms. It's just a precautionary advisory.

This article was released a week ago by a company that deals with genetic analysis and vaccine development, but it's pretty chilling reading if H7N9 ever develops sustained human-to-human transmission.

"Is H7N9 virus a 'stealth virus'"? reports this company's findings that the H7N9 virus has an unusually low number of epitopes.

Epitopes are the unique protein bits that present on the virus envelope. It's what the human immune system "sees" and what antibodies target. Antibodies are also used for quick diagnostic tests. The human immune system could basically be tricked into letting the virus proliferate right under its nose until it's too late and the host is seriously ill.

Few epitopes suggests that vaccines will be difficult to develop and may provide little protection. I've already read elsewhere that H7 strain vaccines tend to provoke a poor immune response to people, even when much larger amounts of antigen (the substances that provoke an immune reaction) are administered in each vaccine dose to a person.

Imagine a pandemic situation where governments are struggling to manufacture enough vaccine to protect everyone as quickly as possible. Instead of a company being able to produce 100 million doses, it's possible that each flu shot would require several times more antigen than usual, thus resulting in a fraction of the 100 million flu shots it could normally produce.

The other alternative is that chemicals that hyperstimulate the body's reaction to a flu shot is added, i.e. adjuvants, so that less antigen needs to be included in each dose. Adjuvants have never been used in US flu shots before and there is some controversy around them. In Europe, the H1N1 vaccine Pandemrix containing the adjuvant AS03 has been strongly linked to hundreds of new cases of narcolepsy in several countries by multiple studies.

The low immunogenicity of H7N9 also means that it could be difficult to develop a cheap, quick diagnostic test if things heat up even more. If a pandemic situation arises, it will be important to distinguish pandemic cases from other illnesses, and that will be hindered by lack of a cheap, quick test for H7N9. That could mean, for example, that limited supplies of antiviral meds could be administered to people who are sick with something other than a pandemic flu.

The Chinese released the genetic sequence from another case. It's missing the mammalian adapted gene from earlier sequences, but it does have a different mammalian sequence that H5N1 research has found increases transmission. Yet another example of this bird flu adapting itself to humans.

It's also another case where mammalian genes are found in a human case, but in none of the bird sequences released so far. This new sample still supports the theory that the virus is picking up these mammalian genes by passing between people.

Although many have praised the Chinese for their transparency, especially in light of how they hid the SARS outbreak until it burst onto the international scene, experts have wondered why the Chinese have released so few genetic sequences from the 91 confirmed cases so far. They certainly have the technological means and capacity to sequence all of the samples very rapidly and publish the results.

"Remember recently that two separate groups of scientists artificially mutated the H5N1 flu strain in their labs to make it easily transmissible in mammals? And the government blocked the publication of their research because they considered the information too dangerous? Well, H7N9 is halfway to acquiring the mutations that the scientists found would make it easily transmissible. "

A flu virus is probably the ultimate bio-weapon - intentional or otherwise. How do we know that HN79 isn't a mutation from a lab? Why do these things always keep popping up in China, anyway :-)

Pete2