BMJ  2006;332:654-655 (18 March), doi:10.1136/bmj.332.7542.654

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MRSA is endemic in some US communities

While everyone panics about bird flu, a more immediate threat is advancing across the USA, says an editorial. The prevalence of methicillin resistant Staphylococcus aureus (MRSA) is increasing rapidly outside traditional hospital settings, and in some communities MRSA is already an established pathogen, especially in children and healthy young adults.

Community acquired MRSA is not simply a hospital MRSA that has escaped. The two best known clones, USA 300 and USA 400, are genetically different from any staphylococci found in hospitals. They behave differently too, causing a wide range of diseases—from minor skin infections to overwhelming and rapidly lethal pneumonia.

The response from doctors and other guardians of the public health has so far been muted, partly because the epidemic has happened so fast. In a recent study in one area of Atlanta, Georgia (pp 309-17), nearly three quarters of all community acquired staphylococcal skin and soft tissue infections were caused by methicillin resistant strains, predominantly the USA 300 clone. Other parts of the US are similarly afflicted.

Unlike their hospital acquired cousins, community acquired MRSA infections remain treatable with a range of antibiotics, including vancomyin. The editorial urges doctors to get to know the pathogen so they can test for it (by culturing samples from skin and soft tissue infections) and treat it appropriately. Many superficial infections have a telltale necrotic patch in the centre.

Ann Intern Med 2006;144: 368-70[Full Text]

Small particle pollution increases hospital admissions among older Americans

We already know that airborne pollution is bad for you, especially the small particles in pollution from traffic, heavy industry, and power stations. Particles with a diameter of up to 10 µm across are associated with increased rates of hospital admission in exposed populations, but little is known about finer particles, even though they are likely to reach much smaller and more vulnerable airways when inhaled.

Researchers from the US exploited two large nationwide databases to look for a link between very small particles (less than 2.5 µm in diameter—PM_2.5) and hospital admissions for heart and lung disease. One database contains all Medicare claims from US citizens over 65; the other records atmospheric concentrations of small particles from monitors placed all over the US.

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Putting the two together in 204 urban counties, researchers found that small particulate pollution was linked to hospitalisation for respiratory infections, chronic obstructive pulmonary disease, and heart disease (especially heart failure) among people over 65. They estimate that every 10 µg/m³ increase in small particle pollution is associated with a 1.28% (95% CI 0.78% to 1.78%) increase in admissions for heart failure among people living a mean of six miles from the monitor.

Although most associations in this study were relatively weak, they do show that this kind of pollution poses an ongoing threat to older Americans. The authors say national clean air standards set by the Environmental Protection Agency in 1997 may not be adequate.

JAMA 2006;295: 1127-34[Abstract/Full Text]

Link between coffee and heart disease could be determined by genotype

Caffeine is metabolised by the enzyme CYP1A2, which has a fast and a slow variant. People homozygous for the fast variant (1A) metabolise caffeine faster than people carrying the slow variant (1F). To find out if coffee is more risky for slow metabolisers, researchers looked for an association between coffee intake and heart attack in a case-control study of adults in Costa Rica.

They recruited and genotyped 2014 men and women with non-fatal heart attack and the same number of healthy, matched controls, and then interviewed them, using food frequency questionnaires. Drinking two or more cups of coffee a day was associated with a significant increase in the odds of heart attack, but only among adults with the slow metabolising genotype. Coffee seemed not to harm the others. Among the slow metabolisers (55% of cases and 54% of controls), the odds ratios for heart attack were 1.36 (95% CI 1.01 to 1.83) for adults drinking two to three cups a day and 1.64 (1.14 to 2.34) for those drinking four cups or more. The corresponding odds ratios for fast metabolisers were 0.78 (0.56 to 1.09) and 0.99 (0.66 to 1.48). The association between coffee drinking and heart attack was strongest in people aged under 50 and was similar for smokers and non-smokers.

JAMA 2006;295: 1135-41[Abstract/Full Text]

Trachoma returns to Ethiopian villages after just one round of mass treatment

The World Health Organization recommends that populations with a high prevalence of trachoma are given antibiotics en masse once a year for three years. Critics argue that one treatment should be enough, but a study from a hyperendemic region of Ethiopia indicates the WHO is right to be cautious.

The prevalence of Chlamydia trachomatis infection in eight villages fell quickly after inhabitants were given a single dose of azithromicin or six weeks of topical tetracycline. Two months after treatment, the mean prevalence of infection among children aged 1-5 years had fallen from 44% to 5%. Slowly but steadily the infection returned, however. Two years after their antibiotics, 11% of children were once again infected with C trachomatis, a predominant cause of blindness worldwide. The researchers used conjunctival swabs to diagnose infection, focusing on children because they are the most vulnerable age group. Infection rates were much lower in a small but random sample of older villagers.

The authors estimate that, after a single round of antibiotics, C trachomatis returns to these vulnerable communities at an absolute rate of about 3% a year. They conclude that one treatment is not enough to eliminate trachoma and its disabling consequences.

JAMA 2006;295: 1142-6[Abstract/Full Text]

Entecavir is a potent treatment for chronic hepatitis B

Chronic hepatitis B remains a serious global health problem despite the availability of effective vaccines. Fortunately, at least five antiviral agents suppress the virus and improve liver function in chronically infected patients. The latest, the guanosine analogue entecavir, could be the most effective so far, according to an editorial.

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The new drug worked better than lamivudine in two randomised trials (pp 1001-10, 1011-20), reducing HBV DNA to undetectable levels in 67% of patients who were positive for hepatitis B e antigen and 90% of patients who were negative. The corresponding results for lamivudine were 36% and 72% (P < 0.001 for both comparisons). Entecavir also produced greater improvements in liver histology and liver function than lamivudine in both groups of patients.

Arguably the most important advantage of the new agent is its track record on antiviral resistance, says the editorial. These studies found no evidence of resistance to entecavir after 52 weeks' treatment. Resistance to lamivudine, on the other hand, develops at a rate of 15-25% of patients a year and is associated with a reversal of any clinical improvement. Other antivirals cause similar problems. Resistance to entecavir may emerge in longer studies—but the short term evidence is encouraging.

N Engl J Med 2006;354: 1074-6[Full Text]

Change in Texas abortion law led to fewer abortions and more births

From 1 January 2000, the US state of Texas banned girls aged under 18 from having an abortion without their parents' knowledge. Over the subsequent two years, abortion rates among 17 year olds, who are subject to the state law, fell by 16% relative to the rate among 18 years olds, who are not.

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An analysis of state abortion and birth certificates also found a small but significant rise in the birth rate—4%—among older minors (mothers aged over 17 years 6 months), who the authors say are most likely to be affected by the law. They say this is the first study to detect a change in birth rate after state legislation enforcing parental involvement in abortion. Thirty five states now have such laws, and the federal government is considering extending them to prevent girls traveling to other states for treatment.

These authors also found evidence that after the Texas law came into force, girls who became pregnant in the latter half of their 18th year were simply waiting to turn 18 before having an abortion. Between 2000 and 2002, they found an increase in the odds of late abortion in this age group (odds ratio for second trimester abortion 1.34 compared with girls over 18; 95% CI 1.10 to 1.62). They urge legislators to consider these observations carefully before tightening the law even further.

N Engl J Med 2006;354: 1031-8[Abstract/Full Text]

Flights are more thrombogenic than movies

Long haul flights are associated with an increased risk of deep vein thrombosis. To find out why, researchers put 71 Dutch volunteers through a specially chartered eight hour flight and an eight hour movie marathon, testing them before, during, and immediately afterwards for markers of activated clotting. To control for circadian rhythm, the volunteers were also tested before, during, and after a regular eight hour day.

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The flight had a significantly greater impact on clotting homeostasis than did sitting for eight hours watching movies, which suggests that the link between flying and thrombosis is mediated by other factors, such as low oxygen tension and air pressure, in addition to simply sitting still.

After the flight, median serum concentrations of thrombin-antithrombin complex (TAT) had risen by 30% (95% CI 11 to 63), compared with a decrease after watching movies and a bigger decrease after eight hours of regular activities. The results for other markers of activated clotting—d-dimer, and prothrombin fragment 1 and 2 (F1+2)—were less dramatic, but still suggestive. Women taking oral contraceptives who also had a genetic susceptibility to thrombosis had the biggest changes in clotting markers after flying.

Lancet 2006;367: 832-8[CrossRef][ISI][Medline]

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