Kathir Palanisamy MD
Faculty peer reviewed
With the recent Christmas day terrorist attack fresh in our memories, the New York Times published an article about some of the health risks of the proposed whole body airport scanners. The two major technologies used in these whole body scanners are backscatter and millimeter wave. Backscatter scanners use ionizing radiation, about 1% of the amount used in dental x-rays. To put this into perspective according to Robert Barish’s book, “The Invisible Passenger,” the dose delivered would be the same as a few minutes in a high altitude airplane. At high altitudes there is much less atmosphere to shield passengers from cosmic radiation. Even so, radiation experts are divided whether this small amount of radiation will collectively lead to more cancer deaths in a large population. Millimeter wave scanners utilize non ionizing radiation, however the image they create are not as clear. Ultimately, we have to decide as a society what inconveniences and possible health risks we are willing to accept in the name of safety. (1)
H1N1 influenza continued to be in the headlines this week with an article in the New England Journal of Medicine about the risks it poses in pregnant women. The study looked at data collected by the California Department of Health about reproductive age women who were hospitalized or deceased in the state of California from April 2009 to August 2009. The study had a couple of noteworthy findings. There was a high incidence of false negatives (38%) in the rapid antigen test as compared to the gold standard of RT-PCR. In addition, later treatment, defined as more than two days after symptom onset with antivirals, led to a relative risk of 4.3 for admission to the ICU or death as compared to early treatment. Thus, the study suggests that even with negative rapid antigen tests, treatment with antivirals should be considered. (2)
Also in this week’s New England Journal of Medicine were two articles focusing on the prevention of surgical infections. The first studied the efficacy of decreasing Staphylococcus aureus health care-associated infections in patients who are nasal carriers of this organism. A total of 917 patients who were expected to stay in the hospital for greater than four days and were identified by real-time polymerase-chain-reaction (PCR) assay as being nasal carriers of S.aureus were randomized to treatment with intranasal mupirocin and chlorhexidine soap versus placebo. All S. aureus strains identified on PCR assay in this study were susceptible to methicillin and mupirocin. The rate of post operative S. aureus infection in the mupirocin-chlorhexidine group was 3.4%, as compared with 7.7% in the placebo group (RR 0.42; 95% CI, 0.23 to 0.75). This relative risk of 0.21 was most pronounced for deep surgical-site infections. This article suggests that the number of surgical-site S. aureus infections acquired in the hospital can be reduced by rapid screening and decolonizing of nasal carriers of S. aureus on admission. (3)
The second study compared 849 patients undergoing clean-contaminated surgery who had received a single chlorhexidine-alcohol scrub versus a povidone-iodine scrub with the primary endpoint of surgical site infection within thirty days of surgery and secondary endpoint of the type of surgical site infection. Clean contaminated surgery is defined as surgery involving the respiratory, gastrointestinal, or genitourinary tracts without leakage or break in aseptic technique. The study found total surgical-site infections were reduced by 40% in the cohort who had received a single chlorhexidine alcohol scrub as compared to the povidone-iodine scrub group. (4)
These studies in this week’s Journal along with the majority of the literature suggests that chlorhexidine-alcohol should replace povidone-iodine as the standard for preoperative surgical scrubs. Interestingly in the chlorhexidine-alcohol versus a povidone-iodine study, the rate of S. aureus surgical-site infections was reduced by approximately 50% in the chlorhexidine-alcohol group despite none of the patients receiving intranasal mupirocin. From a prior study the chlorhexidine-alcohol solution as compared to povidone-iodine has also been found to reduce catheter-associated infections by approximately 50%. The use of intranasal mupirocin and chlorhexidine baths for carriers of S. aureus who have been identified preoperatively by means of a real-time polymerase-chain-reaction assay could be reserved primarily for patients who are undergoing cardiac surgery, all patients receiving an implant, and all immunosuppressed patients. The incremental value of preoperative baths with chlorhexidine alone for all surgical patients still requires further study, but the data reported in these two studies will likely change the approach to prevention of surgical infections. (5)
Turning to general medicine practice related concerns, MDconsult reported on the ADA’s decision to add hemoglobin A1c to the diagnostic criteria for Type II diabetes. The four ways a patient can now be diagnosed with DMII are: the newly added HgbA1c with a cutoff of 6.5%, a fasting glucose greater than 126 mg/dl, a glucose level of greater than 200 mg/dl, 2 hours after 75g oral glucose tolerance test, or a random glucose greater than 200 mg/dl in a patient with symptoms of hyperglycemia. This new addition to the diagnostic criteria is a result of improvements in the standardization of the A1c assay across laboratories, greater convenience of a non-fasting test, the correlation between diagnostic cutoff levels of above mentioned tests and the known threshold risk for development of retinopathy. The downsides cited by the ADA were cost, limited availability in the developing world, and misleading results in patient populations with hemoglobinopathies or inherent alterations in their rate of glycosylation. (6)
Our last stop on this week’s tour of the medical literature is a meta analysis published in Chest which analyzed the cardiovascular safety of Tiotropium in patients with COPD. This meta analysis was done in light of recent findings published in the UPLIFT(Understanding Potential Longterm Impacts on Function with Tiotropium) trial. UPLIFT was a four year randomized, placebo controlled clinical trial which showed improvement in lung function, quality of life, survival, and decrease in COPD exacerbations in patients treated with tiotropium. Results from this trial were also noteable for a reduced risk of fatal CV events adding credence to the safety profile of tiotropium in COPD patients. In this setting a meta analysis of all randomized, double-blind, placebo controlled trials completed prior to 2008 of at least four weeks duration with inclusion criteria of spirometry confirmed COPD, greater than 10 pack year smoking history, and age greater than 40 was done. A review of these trials yielded a total of 19,545 patients randomized to one of two groups: 10,846 to Tiotropium and 8,699 to placebo.
The endpoints were incidence ratios of all cause mortality and composite endpoint of cv deaths, nonfatal myocardial infarction, nonfatal stroke, and sudden cardiac death. The RR in the Tiotropium group of all cause mortality was 0.88 and for CV events was 0.83. Thus, Tiotropium as compared to placebo lowered all cause mortality and composite CV events. (7)
Dr. Palanisamy is a 3rd year resident in internal medicine at NYU Medical Center.
Peer reviewed by Cara Litvin MD, Executive Editor, Clinical Correlations.
1. Wald M. Cancer Risks Debated for Type of X-ray Scan. New York Times: 2010 Jan 8
2. Louie J, Acosta M, Jamieson D et al. Severe 2009 H1N1 influenza in Pregnant and Postpartum Women in California. NEJM. 2010 Jan 7; 362(1):27-35.
3. Bode L, Kluytmans J, Wertheim H et al. Preventing Surgical-Site Infections in Nasal Carriers of Staphylococcus aureus. NEJM. 2010 Jan 7; 362(1):9-17.
4. Darouiche R, Wall M, Itani K et al. Chlorhexidine-Alcohol versus Povidone-Iodine for Surgical-Site Antisepsis. NEJM. 2010 Jan 7; 362(1):18-26
5. Wenzel R. Minimizing Surgical-Site Infections. NEJM. 2010 Jan 7; 362(1):75-77
6. Tucker M. ADA officially endorses hemoglobin A1c criteria for diabetes diagnosis. MD Consult: 2009 Dec 30.
7. Celli B, Decramer M, Leimer I et al. Cardiovascular Safety of Tiotropium in Patients with COPD. CHEST. 2010 Jan; 137(1):20-30