不幸的是，大多數人佩戴口罩不夠堅持，不足以實現這種程度的保護，而美國疾病控制和預防中心(Centers for Disease Control and Prevention)對在醫療場合之外佩戴口罩的態度依然模棱兩可。該機構在自己的網站上給出的結論是：“目前，對於無症狀人群，包括並發症高危人群，在社區中佩戴口罩預防流感病毒方面，我們並不能給出任何建議。”
Q. How effective are antimicrobial “courtesy masks” at preventing the spread of contagious airborne illnesses?
A. The best evidence suggests that, when sick, wearing a mask can help to protect others from getting sick. And when well, wearing a mask around those who are sick will probably decrease your own chances of becoming infected. But the masks are far from foolproof.
Courtesy masks, or what we doctors refer to as surgical masks, were introduced into the operating room in the late 1800s. They quickly became popular among a public eager to protect itself against the influenza pandemic of 1918.
A century later, the advent of modern molecular techniques confirmed that surgical masks can indeed provide good protection against flu. In a 2013 study, researchers counted the number of virus particles in the air around patients with flu. They found that surgical masks decreased the exhalation of large viral droplets 25-fold. The masks were, however, less effective against the fine viral droplets that can remain suspended in the air longer and are therefore more infectious, cutting them by 2.8 times.
Surgical masks also afford fairly good protection for the worried well. In an oft-cited study of 446 nurses, researchers found surgical masks were as good, or nearly as good, at protecting the wearer against flu as respirators, a somewhat more high-tech, masklike device used in hospitals.
The work of Australian investigators provides further support for the value of the simple surgical mask. They estimate that in a home setting, wearing a surgical mask decreases a well person’s risk of getting sick by 60 percent to 80 percent.
Unfortunately, most people fail to wear a mask faithfully enough to achieve this degree of protection, and the Centers for Disease Control and Prevention remains equivocal about the use of masks outside of health care settings. “No recommendation can be made at this time for mask use in the community by asymptomatic persons, including those at high risk for complications, to prevent exposure to influenza viruses,” the agency concludes on its website.
If you don’t have a mask, or don’t want to wear one, standing at least six feet from an infected person will increase your chances for staying healthy. The air surrounding sick people, even if they aren’t coughing or sneezing, is loaded with small infectious aerosolized particles, and the farther you are from them, the better.
Washing your hands frequently, of course, is also critical for staying healthy, since touching infected fingers to the eyes, nose or mouth can transmit infection.
“Population growth, along with over-consumption per capita, is driving civilization over the edge: billions of people are now hungry or micronutrient malnourished, and climate disruption is killing people.” “Population growth, along with over-consumption per capita, is driving civilization over the edge: billions of people are now hungry or micronutrient malnourished, and climate disruption is killing people.”
"We don't have a historical example of a country achieving such rapid reductions in air pollution. It's remarkable," Michael Greenstone the economist and director of the Energy Policy Institute at the University of Chicago who conducted the studies, said.
Diabetes is actually five separate diseases, research suggests
By James GallagherHealth and science correspondent, BBC News
Scientists say diabetes is five separate diseases, and treatment could be tailored to each form.
Diabetes - or uncontrolled blood sugar levels - is normally split into type 1 and type 2.
But researchers in Sweden and Finland think the more complicated picture they have uncovered will usher in an era of personalised medicine for diabetes.
Experts said the study was a herald of the future of diabetes care but changes to treatment would not be immediate.
Diabetes affects about one in 11 adults worldwide and increases the risk of heart attack, stroke, blindness, kidney failure and limb amputation.
Type 1 diabetes is a disease of the immune system, which affects around 10% of people with the condition in the UK. It errantly attacks the body's insulin factories (beta-cells) so there is not enough of the hormone to control blood sugar levels.
Type 2 diabetes is largely seen as a disease of poor lifestyle as body fat can affect the way the insulin works.
The study, by Lund University Diabetes Centre in Sweden and the Institute for Molecular Medicine Finland, looked at 14,775 patients including a detailed analysis of their blood.
Cluster 1 - severe autoimmune diabetes is broadly the same as the classical type 1 - it hit people when they were young, seemingly healthy and an immune disease left them unable to produce insulin
Cluster 2 - severe insulin-deficient diabetes patients initially looked very similar to those in cluster 1 - they were young, had a healthy weight and struggled to make insulin, but the immune system was not at fault
Cluster 3 - severe insulin-resistant diabetes patients were generally overweight and making insulin but their body was no longer responding to it
Cluster 4 - mild obesity-related diabetes was mainly seen in people who were very overweight but metabolically much closer to normal than those in cluster 3
Cluster 5 - mild age-related diabetes patients developed symptoms when they were significantly older than in other groups and their disease tended to be milder
Image copyrightGETTY IMAGES
Prof Leif Groop, one of the researchers, told the BBC: "This is extremely important, we're taking a real step towards precision medicine.
"In the ideal scenario, this is applied at diagnosis and we target treatment better."
The three severe forms could be treated more aggressively than the two milder ones, he said.
Cluster 2 patients would currently be classified as type 2 as they do not have an autoimmune disease.
However, the study suggests their disease is probably caused by a defect in their beta-cells rather than being too fat.
And perhaps their treatment should more closely mirror patients who are currently classed as type 1.
Cluster 2 had a higher risk of blindness while cluster 3 had the greatest risk of kidney disease, so some clusters may benefit from enhanced screening.
Better classification
Dr Victoria Salem, a consultant and clinical scientist at Imperial College London, said most specialists knew that type 1 and type 2 was "not a terribly accurate classification system".
She told the BBC: "This is definitely the future of how we think about diabetes as a disease."
But she cautioned the study would not change practice today.
The study was only on Scandinavians and the risk of diabetes varies considerably around the world, such as the increased risk in South Asians.
Dr Salem said: "There is still a massively unknown quantity - it may well be that worldwide there are 500 subgroups depending on genetic and local environment effects.
"Their analysis has five clusters, but that may grow."
Sudhesh Kumar, a professor of medicine at Warwick Medical School, said: "Clearly this is only the first step.
"We also need to know if treating these groups differently would produce better outcomes."
Dr Emily Burns, from Diabetes UK, said understanding the diseases could help "personalise treatments and potentially reduce the risk of diabetes-related complications in the future".
She added: "This research takes a promising step toward breaking down type 2 diabetes in more detail, but we still need to know more about these subtypes before we can understand what this means for people living with the condition."
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