Britain is in the grip of a new “flesh-eating bug spread by sneezes and coughs”, according to the front page of today’s Metro. The newspaper says that the bacteria are spreading across Britain, as they can be caught through people coughing and sneezing on crowded trains and buses.

This unsettling news put some of the Behind the Headlines team off grabbing their free copy of the Metro at the station this morning, not because of the fear of catching deadly germs from the paper, but because its report was alarmist and overblown. The basis of this news is a laboratory study that investigated why healthcare-acquired meticillin-resistant staphylococcus aureus (MRSA) bacteria rarely cause infections in healthy individuals. The study found that healthcare-acquired MRSA has a high level of antibiotic resistance, but that this property comes at a cost of reduced virulence (being less able to cause infection). Conversely, the study found that the type of MRSA that is usually caught in a community setting is more virulent, but weaker against treatment with antibiotics.

This study has not investigated the transmission, effects or number of cases of community-acquired MRSA in the UK, which formed the basis of many news reports on the research. The researchers state that MRSA outside the healthcare system and in the community is a growing concern, but cases are still very rare. This interesting research contributes to our knowledge of MRSA, rather than warning us of a germ-based Armageddon.

Where did the story come from?

The study was carried out by researchers from the University of Bath and the University of Nottingham in the UK; University College Dublin in Ireland; and Texas A&M Health Science Centre and the University of Texas in the US. It was funded by the UK Medical Research Council and a Biotechnology and Biological Sciences Research Council Studentship. The study was published in the peer-reviewed Journal of Infectious Diseases.

This story was widely covered. Most reports were alarmist, concentrating on the supposed emergence of a dangerous, highly infectious new form of community-acquired MRSA. Many newspapers suggested that transmission is easy, that it can lead to a “flesh-eating form of pneumonia”, and that cases are on the increase. These claims seem to be based on the press release for the research rather than the research paper itself. The study was actually laboratory-based research that had investigated why healthcare-acquired MRSA bacteria rarely cause infections in healthy individuals. Although there was some investigation of community-acquired MRSA, the results do not justify the news coverage.

What kind of research was this?

This was a laboratory-based study. It aimed to examine why healthcare-acquired MRSA bacteria rarely cause infections in healthy individuals. Healthcare-acquired, or hospital-acquired, means that the bacteria cause infections that mostly occur in healthcare environments.

The researchers initially covered the nature of MRSA and how it resists certain types of antibiotics. It is already known that MRSA is resistant to the antibiotics meticillin and oxacillin because it has acquired a piece of DNA called a ‘mobile genetic element’. Meticillin is an old antibiotic that is now no longer used and has been replaced by flucloxacillin.

Many staphylococcus aureus bacteria have now also developed resistance to the penicillin group of antibiotics (because they produce enzymes that can make penicillin inactive), but are usually still susceptible to the antibiotic flucloxacillin. MRSA, however, does not have this susceptibility to flucloxacillin, and is, therefore, harder to treat than most staphylococci bacteria, needing stronger antibiotics still.

One particular genetic element that is key for deciding the properties of MRSA is called the ‘staphylococcal cassette chromosome mec’ (SCCmec). There are several different versions of this cassette, which each provide bacteria with slightly different properties. The researchers state that healthcare-acquired MRSA have type I, II or III SCCmec elements, whereas community-acquired MRSA have type IV and V elements. These different cassettes all contain a gene (mecA) that codes for a protein called PBP2a, located in the cell wall of the bacteria. PBPs (penicillin binding proteins) are a normal part of the cell wall of many bacteria. Many antibiotics work by inactivating PBPs, which cause the bacteria to die. However, the version of PBP encoded by mecA, PBP2a, is less sensitive to antibiotics, allowing the bacteria to survive.

What did the research involve?

The researchers initially determined whether deleting the mecA gene, which encodes the PBP2a cell wall protein, affects the toxicity of MRSA. They then took a healthcare-acquired MRSA strain and a version of this strain that they genetically modified to delete the mecA gene, and performed tests to see how each was able to break up a type of immune cell called a T cell in the laboratory.

The researchers then investigated the ability of the different strains to respond to ‘signalling molecules’, which normally cause the bacteria to activate their production of toxins. The virulence of these strains was confirmed using mouse experiments.

The researchers then compared the production of the PBP2a cell wall protein, T-cell toxicity and the resistance of healthcare-acquired MRSA to antibiotics, compared with community-acquired MRSA.

What were the basic results?

The researchers found that deleting the mecA gene caused the MRSA to become more toxic. This was because the expression of mecA results in cell wall changes that interfere with MRSA’s ability to detect or respond to signals to switch on toxin expression. MRSA with mecA deleted was also more virulent in a mouse model, causing mice to lose weight or die.

The researchers then compared MRSA strains with different SCCmec elements: those with type II elements (typical of healthcare-acquired MRSA) and those with type IV elements (typical of community-acquired MRSA). They found that typical community-acquired MRSAs had lower resistance to the antibiotic oxacillin, were more toxic to the immune system’s T-cells and expressed less PBP2a.

How did the researchers interpret the results?

“As a direct result of its high level of antibiotic resistance, healthcare-acquired MRSA is impaired in its ability to cause infection, which can explain its inability to cause infection in community settings, where antibiotic usage and the prevalence of susceptible patients are low.” In other words, healthcare-acquired MRSA makes a trade-off, sacrificing its ability to spread to healthy individuals in order to fight off a greater range of antibiotics.

Conclusion

This interesting study helps explain why healthcare-acquired MRSA infections are rarely found in healthy individuals. It found that expression of a gene that produces one of the proteins responsible for MRSA’s antibiotic resistance caused it to be less toxic. It also showed that typical community-acquired MRSA strains express less of this antibiotic-resistance protein, but are more toxic.

However, this intriguing lab study did not investigate the transmission, effects or number of cases of community-acquired MRSA in the UK, discussion of which formed the majority of the news reports. On this basis, the research itself does not support the claims that we are under siege from an ‘airborne, bacteria-resistant, flesh-eating superbug’, as newspapers have today suggested.

Links To The Headlines

Flesh-eating bug spread by sneezes and coughs. Metro, February 2 2012

Deadly new superbug is heading for Britain. Daily Express, February 2 2012

New deadly MRSA strain on its way to the UK from USA. Daily Mirror, February 2 2012

Super-strong MRSA bug heading to UK. The Sun, February 2 2012

Flesh-eating bug spread by coughs and sneezes spreading across the UK. Daily Mail, February 2 2012

Links To Science

Rudkin JR, Edwards AM, Bowden MG et al.Methicillin Resistance Reduces the Virulence of Healthcare-Associated Methicillin-Resistant Staphylococcus aureus by Interfering With the agr Quorum Sensing System. Journal of Infectious Diseases, February 1 2012

“Sugar is so harmful that it should be controlled and taxed in the same way as tobacco and alcohol,” according to health experts quoted in today’s Daily Express. The researchers say that sugar indirectly contributes to 35 million deaths a year worldwide.

The news is based on a comment article by US health scientists, who argue that there has been a massive rise in diseases such as heart disease, cancer and diabetes since we began eating more sugar contained in processed food. The researchers argue that many of the health effects of excess sugar consumption are similar to those of alcohol, and that sugar should, therefore, be controlled and taxed in a similar way. They advocate introducing a tax on processed foods with added sugar, limiting sales during school hours and placing age limits on purchase. Interestingly, the authors rate sugar as more dangerous to health than saturated fat and salt, which they call dietary “bogeymen”.

It is important to highlight that the researchers’ article is a comment piece and, therefore, primarily reflects their views and opinions, rather than presenting direct research on the issue. While it is certainly an interesting concept, there is still a lack of evidence supporting the effectiveness of such measures and, crucially, whether the public would actually accept them.

Where did the story come from?

The article was written by researchers from the University of California. There is no information about any external funding. It was published in the comment section of the peer-reviewed scientific journal Nature.

The article was covered fairly by the papers, many of which included comments from UK experts including the UK Food and Drink Federation, which represents food manufacturers. The BBC also quoted an expert from the British Heart Foundation, who reportedly said that taxing salt and fat alongside sugar should also be considered.

What kind of article was this?

This was a comment piece in which experts discuss the global burden of general chronic disease related to sugar consumption and the need to regulate certain dietary items. In particular, the authors draw parallels between the health effects of sugar and the use of alcohol and tobacco, arguing that sugar should be regulated in a similar manner.

It is important to highlight that this was a comment piece only and, as such, it primarily reflects the views and opinions of the authors. A formal systematic review of the literature does not appear to have been conducted and, as such, it is not certain whether all relevant evidence and resources related to sugar consumption and its health effects will have been consulted.

Also, the short piece looks at the issue from a global perspective and, therefore, is not a direct commentary on sugar consumption in the UK. In fact, a map showing average added sugar consumption per day across different nations shows that people in the UK consume a relatively low amount of sugar, at least compared with the rest of the world. Much of the article’s content may be focused on policies suited to the US, which has by far the greatest per-head sugar consumption, at more than 600 calories worth of sugar per day.

What does the article say?

The article points out that, for the first time in human history, non-communicable diseases such as heart disease, cancer and diabetes, pose a greater health burden worldwide than infectious disease. While alcohol, tobacco and diet are all targeted as risk factors for these diseases by policymakers, only the first two – alcohol and cigarettes – are regulated by governments to protect public health. (Although, as it points out, Denmark taxes food high in saturated fats and is now considering taxing added sugar.) The authors argue that fat and salt have become the current “dietary bogeymen” in the US and Europe, but that most doctors no longer believe that fat is the “primary culprit” of such disease. Doctors are apparently calling for attention to be turned towards the dangers of excess sugar consumption.

The authors estimate that over the past 50 years sugar consumption has tripled worldwide, mainly as a result of it being added to cheap processed foods. While excess sugar is thought to be a key cause of the obesity epidemic, they argue that obesity itself is not the root cause of disease but that its presence is a marker for metabolic damage. This, they say, could explain why 40% of those with metabolic syndrome (a collection of the key metabolic changes that lead to heart disease and diabetes) are not obese.

Why do they think sugar is dangerous?

The authors say that although sugar is described as “empty calories”, a growing body of evidence suggests that fructose (one component of table sugar) can trigger processes that lead to liver toxicity and a host of other chronic diseases. “A little is not a problem but a lot kills – slowly,” they say.

The authors argue that sugar meets all the four criteria used by health policy makers to justify the regulation of alcohol. These are:

• Unavoidability. While sugar was only available as fruit and honey at certain times of the year to our ancestors, it is now present in nearly all processed foods. In some parts of the world people are consuming more than 500 calories worth of sugar per day.
• Toxicity. There is growing evidence that excess sugar has an effect on human health beyond simply adding calories and can cause many of the same problems as alcohol, including high blood pressure, high blood fats, insulin resistance and diabetes.
• Potential for abuse. The authors argue that, like tobacco and alcohol, sugar acts on the brain to encourage dependence. Specifically, it interferes with the workings of a hormone called ghrelin (which signals hunger to the brain) and it also affects the action of other important compounds.
• Negative impact on society. The economic and human costs of these diseases place excess consumption of sugar in the same category as smoking and drinking.

What do they think should be done?

While the authors accept that sugar is “natural” and a “pleasure”, they argue that, like alcohol, too much of a good thing is toxic. Strategies to reduce consumption of alcohol and tobacco show that government controls, such as taxation and imposing age limits, work better than educating people. They make several proposals for controlling sugar, including:

• taxing any processed foods with added sugar, including drinks
• reducing the hours during which retailers can sell food containing added sugar
• tightening the licensing requirements on vending machines and snack bars selling sugary products
• controlling the numbers of fast food outlets and convenience stores
• limiting sales during school hours or imposing an age limit for drinks with added sugar

Finally, they argue that regulating sugar will not be easy, but it can be done with enough pressure for change, citing bans on smoking in public places as an example of what can be achieved.

What does this mean for me?

This article will be of interest to food scientists, health policy makers and the public alike, but the use of strategies to restrict the consumption of added sugar is complicated and, indeed controversial. The implications of such moves would need to be considered in both medical and societal terms. They would need both medical evidence to support their effectiveness and assurance that the public would accept drastic changes, such as age limits on buying sweets. For example, in recent years, Denmark has imposed taxes on fatty foods, a move that has divided opinions greatly.

It is generally accepted that added sugar or excessive sugar consumption is bad for health and dietitians advise restricting sugar intake to the occasional “treat”. However, to what extent sugar is directly to blame for the rise in chronic disease and how much is due to other dietary components, such as saturated fat and salt, is open to debate. The current article does not appear to be a formal systematic review of the literature, and it is not certain whether all relevant evidence and resources related to sugar consumption and its health effects have been consulted. As such, it should be considered primarily to reflect the views and opinions of the authors.

In the UK at present, policymakers generally favour encouraging healthier eating through education and the provision of healthier options. This is carried out through public health campaigns such as 5 A DAY or by introducing new food ranges to schools. Whether this approach alone is adequate and whether healthier eating patterns should be encouraged by government regulation, is a crucial area of debate.

Links To The Headlines

Sugar ‘is toxic and must be regulated just like cigarettes’, claim scientists. Daily Mail, February 2 2012

Sugar tax needed, say US experts. BBC News, February 2 2012

Tax harmful sugar. Daily Express, February 2 2012

Links To Science

Lustig RH, Schmidt LA, Brindis LD. Public health: The toxic truth about sugar. Nature, February 2 2012