《The Flu Pandemic and You》是一位加拿大医生写的书，描述大规模流行病的周期。书明明是2006年出版的，但是2020年读下来，完全预测了CONVID-19的发展路径，哎。在这次的疫情之前，我都从来没关注过流行病，毕竟Sars时我还在小学，一点概念都没有。这两周断断续续看完才意识到，流感跟感冒根本不是一回事；流行性传染病从来一直都在，未来也会一直存在下去。就像以前看到的一句挺喜欢的话，说『我不在图书馆，就在去图书馆的路上』，换成流行病，『我不在爆发，就在爆发间隙的潜伏期』。
SARS killed relatively few people, and on a world scale it ultimately had negligible impact when measured in human illness burden and fatality, especially in comparison with the potential impact of a worldwide influenza pandemic. Nonetheless, it disabled health care systems around the world, resulted in massive travel disruptions, and interfered with thousands of people’s personal liberties by way of quarantines and movement restrictions. Its impact upon societies was massive, although the scale of illness was actually relatively small.
Although not all parts of the world may be hard hit simultaneously, the interdependence of economic systems means that disruptions in an industry in one part of the world may affect some linked industry in another country. Disruption may be most significant if events of a pandemic impair essential services, such as power, transportation, and communications.
With every human infection, H5N1 has a new chance to acquire the ability to spread from human to human, potentially bringing us one crucial step closer to an influenza pandemic. Any single human infection is statistically unlikely to result in H5N1 developing this ability, but a greater number of individual human infections increases the probability that this may occur. The increasingly widespread outbreak of H5N1 in birds around the world increases the probability of these individual human infections, each of which is a kind of genetic Russian roulette. A crucial goal in Phase 3 is to curtail the opportunities for the virus to spread from animals to humans and from humans to other humans, and thereby to reduce the risk of a pandemic emerging. Those who are ill must receive high-quality medical care that takes necessary precautions to prevent the spread of infection from those who are ill to others.
Phase 5: There are larger clusters of human-to-human spread, but the cases are still localized in certain geographical areas. In Phase 5, the virus may be becoming better adapted to humans but may not yet be as easily transmissible as it could be. The goal is to contain and delay spread. This is the last real opportunity to avert a pandemic or to gain time to prepare for the start of a pandemic. Travel-related measures can be expected to be used to some degree, as will public health measures within communities to limit and slow the transmission of the virus.
Phase 5 may be signalled by larger clusters in the order of 25 to 50 cases lasting from two to four weeks.
Once we enter the pandemic period, it is virtually inevitable that all countries in the world will soon have pandemic influenza cases within their own borders.
Phase 6 can be divided into Subphases 6a to 6e, which is a classification scheme we have adapted from the Australian pandemic plan. In 6a, the “early” subphase, infections of the new strain of influenza are in the general population but only in certain localized areas of a country. In 6b, the “widespread” subphase, this influenza exists throughout a country and probably most of the world. In 6c, the “subsiding” subphase, the pandemic wave begins to subside. In 6d, the “subsided” subphase, there are no new pandemic influenza cases in a particular area for an extended period of time. Then, since pandemics typically come in waves, comes 6e, the “next wave” subphase, and the cycle repeats. The “next wave” will probably happen several months after the first wave.
In Phases 1 to 5, a goal is to slow the progress toward a pandemic and possibly avert a pandemic. In each successive phase, we are less likely to succeed in stopping a pandemic despite the escalation of public health measures.
Phase 6 cannot be stopped and will run its course, with public health response aimed at minimizing illness, death, and societal disruption.
History shows us that influenza pandemics are recurrent events, although their precise timing and severity is unpredictable.
Travel measures are likely to be used in Phases 4 and 5 and possibly early in Phase 6. There isn’t much evidence of these measures working in past pandemics, except in island nations. However, in past pandemics these measures were mostly attempted in Phase 6, and current thinking advocates their use primarily in Phases 4 and 5.
When individuals and governments face the onset of a pandemic, there will be an intuitive appeal and some good reasons to limit the movement of people across borders, and even the movement and freedoms of people within their own countries and communities. People’s first instincts will be to avoid contact with those who have influenza.
Out of this sentiment may come an impulsive sense that we should “close the borders” and “keep the sick people away!” Travel measures and community containment measures will certainly be used, but we should not implement them in a reflexive and unconsidered way. They must be used quickly and effectively, but with sound reasoning and careful consideration. Travel measures are a daunting proposition: in Canada, over 18 million persons enter our country annually by air, with 91% arriving at six international airports. A similar number depart yearly from our international airports. Our open land border with the United States is crossed over 100 million times each year, in both directions.
Travel measures and community containment measures have human, economic, and societal costs. Also, it must be understood that these measures are very unlikely to stop a pandemic; rather, their goals will be to slow a pandemic and reduce its damaging effects. The costs of these measures will need to be weighed against their expected benefits. There won’t be a one-size-fits all measure to take; rather, the specific choice of measures in the midst of a pandemic will depend upon the phase and other issues.
During Phase 6 of the pandemic of 1918–19, various travel measures were attempted around the world, and none were found to be very effective in slowing or stopping the pandemic. People were travelling largely by rail and ship. With the current extensive use of modern air travel, we expect screening and quarantine of travellers at borders during Phase 6 to be even less effective. If an airline passenger passing through a major international hub like Tokyo, Frankfurt, or Chicago infects a handful of other people who are en route to other destinations around the world with the pandemic strain of influenza, it could span the globe very quickly. No border measures can be depended upon to detect that passenger, who may not even know that she is infected when boarding the plane. No one may know that a novel influenza strain is flying to all continents of the world until it has occurred. Once the pandemic is well under way in Phase 6, most places in the world won’t get much benefit from the more invasive and disruptive travel measures. Despite this, fear and political pressures did result in some countries quarantining travellers who were otherwise feeling well but flew in from a country affected by the 2009 pandemic strain.
It is believed that “exit measures,” applied to ill people who are leaving affected areas, would generally be more useful than “entry measures,” applied to people entering unaffected areas. However, unaffected areas will likely have more popular and political motivation to do things like close borders and impose travel restrictions, while affected areas may have their hands full dealing with other pandemic issues. People in affected areas may want to leave, despite any exit restrictions. So it may be that political impulses and people’s personal fears and actions run somewhat counter to what is actually most useful on a global scale.
If an influenza pandemic starts farther away than it did in the 2009 pandemic—say, in Asia—it will probably take up to a month to build up from a handful to around 1,000 cases at its geographical source, and then perhaps two to four weeks to travel from Asia to Canada. SARS taught us, in Toronto, that all it takes is one case of a new infectious disease to enter a city for that city to experience very significant consequences. First we had one case, which grew into clusters of cases. Within days, the face of our hospitals had changed to one of masks and fear. Since it is not expected that massive border screening or quarantine could succeed in keeping every single case of a new strain of pandemic influenza out of a city, experts feel it is unwise to use a massive amount of resources to implement extensive screening or quarantine programs. Those energies would be better spent elsewhere.
In Canada, public health officials have concluded that entry screening at borders for SARS during the 2003 outbreak was not successful or cost-effective. The data from four Asian locations and Canada indicated that body temperature-sensing devices did not detect a single case of SARS in the screening of over 35 million entering travellers. Arrival screening, applied to people entering an unaffected area, is not generally recommended but is likely to happen anyway in some places. There’s less scientific evidence that it’s useful.
What about quarantining everyone coming from a pandemic-stricken area? This has intuitive appeal, but the logistics are staggering. In our era of high-volume air travel, with 1.4 billion air travellers per year and 25 persons per second crossing national borders, it would mean placing tens of millions of people worldwide in quarantine facilities for days, where they must be fed, kept clean and warm, and kept safe from infecting one another. This is unworkable. Remember that an influenza pandemic will not be a brief event but will go on for months or years. Meanwhile, all it takes is for one case to slip through. There are better ways to use public energies and resources.
The WHO does not generally recommend a complete closure of international borders or travel prohibitions. It is judged to be excessively resource intensive, hugely economically disruptive, and probably not successful in the end. Absolute border closures would cripple modern economies, and most countries depend upon trade not only for their economies but for food, medications, fuel, and other essential goods. In most places, public energy is better employed doing things that have a better chance of success, such as early detection, treatment, and isolation of the first cases, contact tracing, and community containment measures.
To infect you, influenza must enter your body through mucous membranes: your eyes, your nose, or your mouth. The relatively large droplets containing influenza virus can directly infect you if you are less than 1 metre from an infected person. This may happen if an infected person sheds virus while coughing, sneezing, or talking and the virus particles enter your eyes, nose, or mouth. Droplets may also deposit themselves on an object; if you touch this object, you then bring the virus to your own mucous membranes by touching them.
Handwashing is the single most powerful personal measure that can reduce your chance of contracting influenza during a pandemic.
This is what happens: People with influenza cough, clear their throats, talk, or sneeze on their hands. They open doors and push elevator buttons. They may not realize they’re sick, because a person with influenza can be contagious and shedding virus particles one day before any symptoms appear. Influenza virus particles can survive on inanimate objects: up to 48 hours on hard surfaces, up to 12 hours on cloth or tissues.4 You open a door or push an elevator button in the wake of someone with influenza, you might rub a bit of dust from your eye or scratch your nose. Now, you may have infected yourself with influenza.
Avoid using overly hot water, because repeated use of hot water can irritate and cause dry and cracked skin.
In everyday life, influenza virus particles travel in droplets larger than 5 microns in diameter, which are released or “shed” from infected persons when they sneeze, cough, or talk. These are large droplets. This is an important detail, because large droplets do not travel very far. It is thought that they spread no farther than 1 metre, which is the basis of the “less than 1 metre” principle: the distance that people should stay apart to limit the risk of infection. Other types of infections, like tuberculosis and chicken pox, can travel in “aerosols,” which means they can be suspended in smaller particles with the ability to travel farther.
The “less than 1 metre” principle of the travelling distance of large droplets and the transmission of illness is drawn from good scientific evidence. It comes from studies of the spread of meningococcal disease, a cause of meningitis, in army barracks and class-rooms.2–3 Meningococcal disease spreads in a fashion similar to the way influenza spreads. Early in the 20th century, an outbreak of meningitis in a military camp was controlled when the space between soldiers’ beds was increased from 15 centimetres to about 1 metre. In 1982, during a meningitis outbreak in a school in Houston, a distance of less than 1.02 metres between student chairs in the classroom was found to be a risk factor for the spread of meningitis.
Masks may have a role as part of your personal protective strategy, but both their potential advantages and their limitations must be understood. They are not essential, and universal public mask usage is not advocated in the Canadian or American pandemic plans, even during Phase 6 of a pandemic. Masks are, in large part, a personal choice. There is clearly no reason that anyone should be going about her daily life wearing a mask during Phase 3 (unless she is suffering from a case of the novel strain of influenza, but then during Phase 3 she should be isolated in hospital). Specific situations may have specific issues. For example, if you are boarding an airplane leaving an area affected by a novel strain of influenza during Phase 4 or 5, the WHO does recommend that the airline offer you a mask, because this setting poses particular risks.
Consider a good “surgical,” “procedure,” or “isolation” mask if you must be in a crowded situation. At this time, there is no evidence of the need for an industrial or particulate respirator such as an N95 mask. If you are going into a crowded subway in Phase 6, a mask would be a good idea. For a walk outside in a quiet open park, a mask would not be needed.
If you do need to take public transit, try to use it during off-peak hours, so that you don’t need to be as close to as many people.
Here’s the way you should look at it: If someone told you that you were going to spend some time in a room with a person who has influenza, and you had a choice of either sitting half a metre away wearing the best mask in the world, or sitting 3 metres away without a mask, we think you’d be better off sitting 3 metres away, unmasked. If you had to sit half a metre away from that person with or without a mask, you should take the mask.
Get “surgical,” “procedural,” or “isolation” masks that are comfortable and fit your face well. You don’t need N95 or “submicron” masks or industrial respirators, which have better filtration but are more expensive. N95 and submicron masks are hot and stifling, and we can tell you from personal experience that you will have a constant desire to rip them off your face. The wearer of an N95 is much more likely to fiddle with it and try to reposition it, or take it off “just for a second,” all of which can lead to its contamination or complete failure as a protective device. In Toronto during SARS, N95 masks became the standard device used in health care settings because it was unclear at the outset how SARS was transmitted; but for most diseases including influenza, they are unnecessary. N95 masks are necessary for much smaller aerosol particles, which occur with tuberculosis, chicken pox, and measles; they are unnecessary for diseases like influenza, since the current scientific evidence indicates that influenza in everyday life is mostly transmitted by large droplets, not by aerosols. You may see health care workers advised to use an N95 mask at times during a pandemic, but that would be related more to their closer contact with patients.
The best advice is: Don’t do it. It’s like reusing a condom—obviously a bad idea from both infection control and aesthetic points of view. However, we recognize that during a pandemic, some people may want or need to reuse their masks if there is an insufficient supply. Some people may be taking care of sick family and loved ones, and may simply not be able to get more masks, so reuse may be the only viable strategy. A used mask may be better than none in caring for an ill family member. There is no scientifically based guidance that we can give you on reusing your masks.
However, if you’re going to do it anyhow, here’s what we think makes sense. Don’t share masks. If you are using them in your household, label them so that it is clear whose masks are whose. The influenza virus can survive on objects for some time, so try not to wear a particular mask again until several days after you last wore it. Have a number of masks, so that you can rotate through them in sequence. Disposable masks are not designed to be washed, so don’t wash them—after each use, just hang each one up and leave it for a few days. Inspect masks before reusing them and discard any visibly damaged or soiled ones. Understand that reused masks provide substandard protection, so you really shouldn’t do anything with such a mask that is not so crucial that you would do it even if you didn’t have any mask at all.
Masks are single-use devices, intended to be used for a few hours. Once they become wet with condensation from breathing, they are less effective. To go through a pandemic wearing fresh masks all the time, one would need thousands of masks. Masks are susceptible to damage. If they have small tears, damage that isn’t visible to the naked eye, they no longer provide the same degree of protection, which may result in your feeling an unwarranted sense of safety from wearing a damaged mask. Masks themselves can become contaminated. Then your mask is an object that can contaminate you and that happens to be sitting on your face.
The biggest pitfall would be if a mask reduces your adherence to staying 1 metre away from other people or decreases your attention to the more important activities of handwashing or cough and sneeze etiquette. Those other measures are really still the core actions to reduce one’s chance of contracting influenza or spreading it.
Third, and most important, in health care, gloves are not considered to be a substitute for the essential activity of handwashing, which is still the cornerstone of infection control. There is a danger that by using gloves in routine daily life, a person might acquire a false sense of security and employ less optimal handwashing. Finally, if the gloves become contaminated and are still being used (remember, they are meant to be single-use and disposable), you could be contaminated by the gloves themselves, while you are under the dangerous and mistaken impression that the gloves are providing protection.
The core action that you can take is frequent hand-washing, with special care to wash your hands before touching your own mucous membranes. If you decide to use an object of some kind to manipulate other objects around you like elevator buttons and doors, we cannot say there is evidence to recommend this. What we can say is to beware of the contamination of that object itself. Perhaps carry it in some kind of holster or sheath, so that it is more difficult for this object to contaminate other things that you might be carrying or using. Above all, do not view this as a substitute for handwashing, which remains a central action.
Choosing how to go about your daily life during a pandemic means striking a balance between an activity’s risk of exposing you to influenza, and whether that activity is essential for you.