posted
Why is there a flu season? In the northern hemisphere it correlates with winter months. Is there a causal relationship there? If so, why? Is it really a question of cold weather depressing people's immune system? If so, do we know *why* cold weather taxes the immune system?
For Hatrackers in the southern hemisphere, does your area of the world experience a flu season? When is it?
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posted
Noemon, my understanding is that influenza has a "season" for the same reason colds have a "season" -- i.e., droplet transmission is exponentially diffferent in close crowded quarters, such as we have in cold weather. The viruses are there in the environment all the time (although in the case of flu, they are being incubated in other animals and mutated). That's why you could get a cold in summer, although it's rarer.
There are more species of cold virus (100+) then there are new flu viruses. Once we start grouping together, any cases of newly mutated flu (for which we have insufficient antibodies as herd immunity) can spread rapidly, but as people get exposed, they develop antibodies, whether or not they come down with a full case or even any noticable symptoms. Thus the herd susceptibility drops and those who have not yet been exposed are more protected by vector default. That is, until people start catching a new mutated form when in enough proximity to reach critical mass for a new "season."
This, at least, is how it was explained to me. I'm not sure I find this totally convincing (what about, e.g., military barracks and nursing homes, where there is virtually constant proximity), but it just may be that the "critical mass" to spread a breakout faster than people can clear it individually is insufficient until a larger part of the total population is in close quarters.
I'll look around. Had you checked the CDC?
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posted
I'd expect the "flu season" to correspond to the cold weather season on any given continent. I'm curious as to whether this has been found to be true for non-NA Hatrackers.
I know the flu season in China precedes ours, because the formulation of the flu vaccine in the US is based on the Asian flu characteristics. I believe the CDC "targets" our vaccine to cover the main strain(s) seen elsewhere in the world, i.e. where the cold weather season precedes ours.
BTW, viral antibodies to one cold strain don't seem to protect too well against most others. Thus, colds get passed year-round (although less requently in warm-weather months). But usually only one or two strains of flu become predominant in spread, and there is (I think) more crossover for antibody reactivity. Thus once it has swept through, you are less likely to get it until the next "critical mass + new strain" peak.
[ October 06, 2004, 10:05 AM: Message edited by: Sara Sasse ]
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posted
Nope, hadn't checked the CDC, or anybody else for that matter. I just got to thinking about it last night, and thought that I'd see what you and Theca had to say (is Theca still around, by the way? Haven't seen her in a long time, it seems).
quote:This, at least, is how it was explained to me. I'm not sure I find this totally convincing (what about, e.g., military barracks and nursing homes, where there is virtually constant proximity), but it just may be that the "critical mass" to spread a breakout faster than people can clear it individually is insufficient until a larger part of the total population is in close quarters
Yeah, the whole "closer proximity" theory occurred to me, but it doesn't quite seem plausible to me, for the same reasons that you expressed skepticism of it. I mean, I'm really not in any closer proximity to other people in the winter than I am at any other time of the year. Are most people? I work with the same people, in the same office, year round. The critical mass argument came to mind too, but honestly I'm having trouble coming up with many populations that are really in significantly closer proximity in the winter than in the summer. Can you think of some that are? In fact...if anything, I'm more isolated in the winter than I am in the summer; I'm more likely to just stay home rather than brave the elements, so I probably go to the store, the movies, restaurants, etc. less during flu season than I do during other parts of the year.
Dana, good luck with the flu shot. As a result the British gov't revoking vaccine manufacturer Chairon's license yesterday (or was it Monday), we're only going to be getting 50% of the flu vaccine that we got last year. Given the projected shortage, doctors are being asked to vaccinate at-risk patients, such as pregnant women and the elderly, first.
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posted
My doctor counts me as high priority for the shot because of my asthma and becasue I visit a lot of elderly folk in their homes, nursing homes, and hospitals. So I haven't ever had too much trouble getting one. Two years ago I had to wait a couple weeks, but that was it.
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posted
Wow, people are posting quickly. My post was written immediately after reading Dana's.
I don't get flu shots myself, generally. Given that I have mild asthma my allergist always recommends that I do so, but I'm not wild about getting shots, or really taking any kinds of drugs at all, so I generally don't, and I generally don't get the flu*.
I don't have any special fear of needles, but I don't have any great love of them either. Well, that's not quite true. I love that we *have* them--they're a great way of getting drugs directly into the bloodstream--but I don't get any joy out of being stuck with one.
*"the flu". Isn't it funny how we use the definite article with some diseases, but not with others? It seems like an archaism to me--I think that it was much more common to use "the" with disease names in the 19th and early 20th century than it is now.
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posted
WHO has an interesting factsheet with (among other info) external links to information on areas with year-round transmission of influenza. This does seem to correlate with areas of high population density.
I know it seems like we are more isolated in winter, but in winter we are very enclosed wherever we go. Car windows are closed, shops use double-door systems to keep out the cold air, hotels switch to revolving doors (except when necessary), and air is recirculated in public building to conserve heat and cut down on fuel costs.
I still don't know if I'm convinced, but there are a lot of hidden circumstances for repetitive exposures, if you think about it.
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quote:Disease spreads very quickly among the population especially in crowded circumstances. Cold and dry weather enables the virus to survive longer outside the body than in other conditions and, as a consequence, seasonal epidemics in temperate areas appear in winter.
Interesting. First I'd heard of that -- the opposite as for most pathogenic bacteria, it seems. Hmmm.
posted
I've always wondered if anyone had ever done a study comparing flu rates in areas like NYC and Chicago (where the temperature drop is precipitous, and thus people cluster more; businesses are more likely to trap the warm air; and the cold-dry-weather would be more noticeable) versus places like the Southwest.
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posted
Ohhhhh, I hadn't thought about air in buildings being recirculated. That could account for it right there. The other examples you were listing don't really sway me though--given the ubiquity of air conditioning, most people I know drive with their windows up in the summer as much as they do the winter, and shops seem as intent, to me, on keeping the hot air outside in the summer as they are keeping the cold air outside in the winter. What other hidden circumstances are you thinking about?
The whole business with the recirculated air would only apply in modern times, while the other hidden circumstances you were mentioning would seem to me to have stopped applying in the recent past. It would be kind of funny if we'd swapped one set of circumstances of transmission for another.
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posted
I was just talking to a friend of mine who is a heating and air guy, and he said that air recirculation is a constant in both heating and cooling systems--air is recirculated in buildings in the summer just as much as it is in the winter, it would seem.
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posted
Good points, Noemon. I'm just thinking aloud, as I vaguely recall asking questions about this in medical school and being unsatisfied with the answers. There may well be a lot of unacknowledged hand-waving going on here.
I know many stores use air-conditioning, but there definitely seem to be more people out and about (spending time just window-shopping, eating at outside tables) in the summer as compared to winter. We seem as a work culture to be more likely to eat in at the office (brown bag, order delivery) rather than brave icey streets and tramp through slush. When we do visit friends, it's directly into the house rather than hang around outside on the porch or around the grill.
I think we also tend to wash hands less frequently, both because of chapping and because they don't get as dirty outside in mitts or gloves (and remember that the first vector for influenza spread is usually children). Plus, if dry air really does facilliate the length of infectiveness of particles outside the body, then both the outside and inside (heated->drier and frozen->drier) environments would be more infectious in winter.
[ October 06, 2004, 10:53 AM: Message edited by: Sara Sasse ]
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posted
Oh, yeah, Sara, I completely understand that you're just thinking through this aloud--so am I. I hope it didn't seem like I was being argumentative for argumentativeness sake, or otherwise unplesant in any way. I'm actually having a great time thinking through this, and am delighted to have you around to work through this with. I'm having a lot of fun thinking about this; this is the kind of thing I love to do.
posted
I don't get flu shots, and I don't get them for my kiddos either. I just have a problem with putting yet another thing into our bodies. We're all in good health, and neither of my kids have ever had the flu. Guess that makes me lucky.
posted
I heard an NPR report this morning that the CDC (or whomever) is asking that healthy adults not get flu shots this season because of a shortage of shots caused by a manufacturing problem in England. Shots should be reserved for the elderly, children and those with breathing problems.
The shortage sounds acute -- the U.S. supply of flu shots will be half of what was expected. But the report also said that the government was not asking U.S.-based firms to begin or increase production, instead choosing to issue this advisory.
It also said that part the supply problem has been "aggravated by increased demand for flu shots."
Ummmm. If there's increased demand, shouldn't that mean that, you know, there should be increased supply?
I realize that flu shots aren't "moneymakers" for drug companies, but how come the government can't ask U.S. manufacturers to step up production?
I normally get a flu shot. They really work for me. I used to get sick 2-3 times a winter with at least one of those being the type of flu that knocks you out of commission for 2-4 days. After I started the flu shot regimen three years ago (because my wife had contracted pneumonia the previous winter as a result of a flu she contracted from me), I haven't had the flu at all and at most get one cold during the winter.
I haven't decided what to do yet. With my family unit consisting of a not-yet-one-year-old and a wife who is *somewhat* at risk, I think I could justify it.
But what would be better is if the government would stop being stupid. Even flu shots that are administered as late as early January can be worth it. Posts: 3423 | Registered: Aug 2001
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1. My guess is that air travel during the holiday season (and in general) helps spread the flu viruses. My guess is that it's why during the first part of January certain areas of the county all of a sudden have an outbreak of flu cases.
2. Recirculated air not only could spread the virus, but it also dries out the sinuses (esp. heated air) which I believe would remove one of your defenses against infection. Plus for those of us with sinus problems it can lead to sinus infections or problems that lowers our defenses and make us more susceptible to infection.
At one point I worked in an office where an air vent was directly over my workspace -- I was always having sinus problems.
Now I work in a World War II-era building. It's great. Sure, I may be sucking up the asbestos but the thing is heated by radiator (no air conditioning, but we're in SF's fog belt so it's usually not a concern) so my only sinus problems come from pollen and pollution.
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posted
Hey, have you guys heard that we're only going to be getting half of the amount of flu vaccine we got last year?
Zal, those are good and interesting points--I hadn't thought about that. All of those things you were talking about are products of life in the modern era, though, so if they're the cause of flu season, I expect that the historical record would show that the flu season is a fairly recent development. Sara, any idea if that's the case?
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posted
I don't know that flu season is a recent development, but there's no doubt that air travel has increased the speed with which Asian-based flu viruses have spread to the U.S. and other countries on this continent.
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quote:You know, I read in the paper this morning that the flu vaccine supply will be cut in half this year.
Really Sara? I wish someone had told me about that earlier!
I've been digging around on the WHO site all day (as time has permitted), and have been having all sorts of fun with it. Thanks for the link by the way.
So far, the only history related stuff I've found has talked about the years of major flu outbreaks, rather than the time of year at which the occurred. One interesting fact that I did turn up was that the Spanish Flu Pandemic of 1918 started in March of that year in N. America, and had spread to Europe by the following month. (link).
quote:*curious about the circumstances that led to Sara stitching herself up... twice.
First time was running to a delivery with my intern, when we hit a slick patch (pudding? I hope) on the stairwell and both tumbled down half a flight. He twisted an ankle, and I tore up my knee through the scrubs. I had to leave him behind (he limped into the delivery room a bit later) while I went to the baby. Someone saw blood dripping down my ankle & when I had a chance, I took off the gear and found a shredded place with some subcutaneous fat showing. No joint damage, though, so I trimmed it up & washed with betadine, set up a sterile field, and threw in a few stitches.
(The line-up at the ER was murder, as it was flu season, and it would have been hours before I could have gotten seen officially and discharged. We had too many babies waiting in the wings - a couple sets of twins - and a good number of residents were already out for the count, so backup was sketchy at best. This was also a very simple repair.)
The second time was after I cut a finger open down to bone on a catfood tin can lid. The first time, I went to the ER & had it stitched. She stitched it too tight (fingertip white), and when I took out the stitches a week later, it re-opened. (Not enough blood flow for adequate healing and so tight on the surface that the subcutaneous area had buckled open under the stitches.) So I redid it right.
I almost sewed up a toe once after I slit it open on the edge of a mirror, but Urgent Care was open and I didn't have the right supplies. Good thing, too, as I flinched a lot while she sewed it, and I probably wouldn't have held still enough for myself. That toe was painful!
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posted
Damn Sara! Tell me you used a local anesthetic when you were stitching up your knee! Please! If you didn't, consider lying to me about it. (only sort of joking)
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posted
Um...ouch. Squick. I make my husband remove any splinters the kids get, becuase it squicks me out so much. He has to take them to the doc if they are, say, getting a hematocrit. He has to come to the midwife with me when I get a blood draw. I find the blood draw worse than labor. (shudders)
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posted
For half a second I read that “no” as “no I didn’t use a local anesthetic” followed by “I used an anesthetic,” which, by process of elimination must be a general anesthetic, and my brain couldn’t figure out whether to be impressed or confused. Fortunately it settled on confused, which led to me figuring out what you actually meant.
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The thought of you stitching on yourself without anesthetic was almost physically painful for me. I honestly don't know if I could stitch myself up, even if the area were numb.
In my experience, it's harder to properly numb areas that are near the bone, like a toe. I'm not sure why that would be the case, but for me it has been.
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posted
I am reading a fascinating review (Influenza: Emergence and Control) from last month's online edition of the Journal of Virology. I will edit this post with any relevant excerpts.
posted
Some things I'd prefer not to be given a local anesthetic for. Actually, make that in some cases, as it is usually dependent on the person doing the anesthetizing. You usually use a couple milliliters of fluid at least, and if injected quickly, that just spreads apart the tissue in a very painful way. The lidocaine also burns, but you can cut that way down by adding some sodium bicarbonate to the mix -- but again, this increases the volume.
However, the right mix injected slow and steady is amazingly virtually pain-free. I'm serious. When I can talk to kids and get them to understand that they have to hold realllly still, I can give the anesthetic over a period of minutes rather than seconds, and it numbs the area that is about to be stretched before it happens. The ER docs hated that technique, though, because it meant I spent longer time with the patient, and they didn't believe it was safe to stand there holding a needle in a kid's skin.
Shows what they know about kids. Right kid with the right preparation --> a heckuva a lot safer than just pinning them down and traumatizing them.
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posted
Really? That's so interesting Sara! Even when the injection is given close to the bone it can be painless? Huh.
::wishes that through the miracle of time travel, Sara could go back to the early 70s and be my pediatrician::
You know, Christine just had a root canal attempted by her dentist. It was pretty unplesant, with the shots being unusually painful. I'd been wondering what it was about the shots that made them hurt more than usual.
Anyway, the attempt failed, and she had to go to an endodontist. He gave her a sniff of nitrous oxide before he gave her the novacain injection, which completely took care of her paying attention to any pain she might have been feeling.
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posted
Noemon, I bet he was rushed. The tissues in the mouth are pretty tacked down with stiff membranes, so you reallly feel the stretch & rip as the tissue accomodates.
I actually learned how to give good local anesthesic control from a Canadian dentist. He did it slow, and I hardly noticed. So I pinned him down for tips.
The periosteum (outer covering of bone) is exquisitely sensitive, so if you scrape it with the needle right away, it is going to hurt. But you can flood the area with lidocaine before you get to the bone, if you do it slow and steady.
[Mind you, if the bone is broken, then you have to block the whole area from above. Nothing else works. But on a distal extremity (e.g. a Bier block for a broken wrist), this technique may require enough local anesthetic that you have to use a tourniquet (slowly deflated in gradual pumps) in order not to stop the heart by letting enough flood into the bloodstream at once. It's complicated, but it works, and I've happily chatted with kids about Spongebob while the orthopedist set their forearm.]
The real problem with anesthetic is when you have crushed tissue, because the acidity of the area makes the anesthetic less effective. So if you want a good block, you have to know where the nerves run prior to the crushed site and then block the nerve itself that supplies the general area.
[ October 06, 2004, 03:22 PM: Message edited by: Sara Sasse ]
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quote: <-- volunteers her veins to young, terrified students to practice starting IVs
Sara!!
I can't imagine that. Maybe it's because I have shy veins. I have to be squeezed and manipulated to the point of purpleness before they can even tap a vein. Then they have to wake me up.
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I though I had read most of the posts on this thread, but realized that I skipped over the section where you were talking to dkw. And then I messed up your name.
Sorry.
And seriously: how come the government is refusing to ask U.S. manufacturers to make more flu shots?
----- On shots: When I was in Romania I had to get a gammaglobulin shot every three (four?) months. At first it was okay because there was a local LDS member who was a nurse. She would talk to you -- and esp. ask questions -- while she was preparing the shot and you had to concentrate on answering them so it made it easier to not focus on the shot and tense the muscles. Her shot delivery was also effective, she'd be talking to you and then you'd feel a slap on your upper thigh and then stick in the needle. It totally worked. They were the most pain-free (heavy duty) shots I've ever received.
Later, a humanitarian missionary from the states administered our shots. I believe she was a nurse, but she could not give a good shot. The worst was once where she stuck it way up on my buttock -- just below my lower back. It hurt like hell and it took forever for the globulin dissolve.
Although that wasn't quite as bad as what happened when my wife went to get a flu and pneumonia shot. We went to one of those things where they set up a table in a drugstore/supermarket and you sit in a chair and get the shot. The first shot in the left arm went okay. But then instead of moving around to the other side, the nurse reached around my wife and stuck the second shot in her right arm. Needless to say it went in at a weird angle and it took longer than normal to deliver the contents. My wife's arm was sore for a week afterwards.
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posted
I had a dentist only inject the anesthetic in one spot on a gum before drilling. Every other time I've gotten it, I've had at least 3 or 4 separate injections. I was scared to death he'd forgotten to finish, but there was no pain.
Does that mean he got the nerve and that blocked the sensation for the whole section of my mouth?
posted
Mack--I'd say so, since being around the elderly is one of the reasons that Dana qualifies for a shot.
quote:I actually learned how to give good local anesthesic control from a Canadian dentist. He did it slow, and I hardly noticed. So I pinned him down for tips.
You know, there are *so* many elements to these three sentences that just come staggeringly close to qualifying for the OOC thread, but Sara manages to skate within a fraction of a nanometer of the line without crossing it. That, my friends, is talent.
Fascinating information by the way Sara; I love it when you share stuff like that.
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posted
Zal, no problem on the name--people mess up my name here all the time. I knew you were addressing me, so no worries. Also, I didn't mind that you and Dan brought up the vaccine shortage story as though it were new information; I figured you'd just skimmed that part of my post, and saw the opportunity to make a joke.
I'm not sure why the US hasn't taken steps to mandate that drug companies produce an adequate supply of the drug, but I suspect that it boils down to a lack of money, as such things usually do.
Am I right in thinking that the cultivation of vaccine in eggs is incredibly outdated technology, and that there are much more efficient means by which the vaccine could be produced?
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posted
Making flu vaccine takes a long time; five months, with the most common current method. (Link) So it's not like the US government -- or anyone else -- can just demand that a manufacture suddenly churn out a new batch.
quote: Manufacturers use approximately 90 million eggs for each strain—too many to order quickly when the breakout of a new strain takes health officials by surprise.
. . . or when there is some other sudden problem with the supply.
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posted
You know, I knew that at one time, but forgot.
Thanks, rivka.
I do understand that there have been problems in years past where flu shots have beeen manufactured but the demand wasn't there so many of them went to waste so I understand why drug companies don't want to necessarily increase production even though demand appears to have increased.
But there's got to be a better way to do this. I mean isn't the cost of wasted flu shots less than, say, the cost of giving emergency medical care to a ton of flu victims.
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The following is an excerpt from "Influenza: interspecies transmission and emergence of new pandemics" in FEMS Immunology and Medical Microbiology (August 1997), by some of the same authors as the article above. Notably, this article represents a collaboration between St. Jude's research center and the University of Hong Kong. The information is more accessible than the article from last month's Journal of Virology, where the technical details were very complicated. Basically the same stuff, though. [bold added by me for emphasis]
quote:It has been 28 years since we had a human pandemic, and it is certain that there will be another. Where will the next pandemic stains come from? The accumulated evidence indicates that these viruses will come from aquatic birds. After the Hong Kong/'68 pandemic, the National Institutes of Health and World Health Organization decided it was time to find out where these viruses came from, and we and others have been involved in elucidating the world reservoirs of this virus.
Important clues were provided by studies done in the early 1970s in Canada, which found that, prior to their migration south, about 25% of young ducks tested from mid July to late August carried influenza virus. Duck infection is very different from human infection; there are no disease signs and the virus replicates in the intestinal tract more than in the respiratory tract. Shedding virus in their feces, these ducks make a wonderful system for transmission. As they migrate in the fall, they fly over turkey farms in the United States contaminating water as they go and probably infecting many turkeys on those farms. Similar avian reservoirs of influenza virus have been found all over the world, wherever studies have been done.
We do not know how influenza viruses are perpetuated, because the virus does not establish chronic infection in individual birds. In fact, it barely remains in the population, almost disappearing by the end of the season. But in the springtime other aquatic birds, migrating from South America, pick up these viruses and they, in turn, shed them in their feces onto the shore line. About 25% of ruddy turnstones and redknots, migrating from South America to the north slopes of Alaska, were found to be infected and capable of dropping viruses in their feces on the beaches [2]. Thus the biology suggests that the influenza viruses are transmitted to a limited range of other avian hosts. ... Phylogenetic data also support the notions that avian species are the origin of all the mammalian lineages; there is geographical separation of the lineages; and the avian strains are in evolutionary stasis. In contrast to the mammalian viruses that are constantly changing their antigenic properties, some of the avian strains have not changed their antigenic epitopes in 50 years.
The full text explores the difficulty of transmission of purely avian strains to humans without another mediating vector, such as pigs, being infected as a host vector first. They've traced out the genetics to show where swine flu genome parts were incorporated into the human-infecting strain.
Wow. I'm floored.
Bird poo? Amazing.
[ October 06, 2004, 04:05 PM: Message edited by: Sara Sasse ]
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