MRSA DIFFERS IN COMMUNITY, HEALTH CARE SETTINGS

Methicillin-resistant Staphylococcus aureus (MRSA) infections are usually associated with hospitals and long-term care facilities, as well as with invasive procedures, such as dialysis and the insertion of indwelling catheters. However, MRSA infections have recently been identified in the community, which raises the question: Have these infections been transmitted from the hospital, or are they caused by different resistant strains?

A recent prospective cohort study by Naimi et al examined both health care– and community-associated cases of MRSA. The investigators found distinctly different isolates of MRSA in the two settings.

Twelve laboratories in Minnesota identified 1,100 patients with MRSA, whose medical records were then reviewed for additional information regarding their infections. Cases were defined as either community- or health care–associated, based on whether the patient had been treated in a hospital or long-term care facility, or had had surgery, dialysis, an indwelling catheter, or a previous known positive culture for MRSA. The infections were health care–associated in 937 patients (85%) and community-associated in 131 (12%). Thirty-two could not be classified due to lack of information.

Compared with health care–associated MRSA, community-associated cases involved more skin and soft tissue infections, and fewer respiratory and urinary tract infections.

Pulsed-field gel electrophoresis was performed on 106 community-associated isolates and 211 health care–associated isolates. Five clonal groups accounting for 96% of all isolates were identified, and their frequency was calculated. Isolates from clonal groups A, B, and H were responsible for most of the MRSA cases in the community and health care settings, but their distribution in these two settings was markedly different.

The authors noted that the difference in characteristics—both demographic and clinical—between community- and health care–associated MRSA suggests that in the community, MRSA infection is not a result of exposure to MRSA strains common to health care settings.

Naimi TS, LeDell KH, Como-Sabetti K, et al. Comparison of community- and health care–associated methicillin-resistant Staphylococcus aureus infection. JAMA. 2003;290: 2976-2984.

LOW CIGARETTE TAR LEVELS DON’T LOWER CANCER RISK

The amount of tar per cigarette has decreased from 37 mg in 1950 to less than 7 mg in today’s very low tar brands. Although previous research has demonstrated that the risk of lung cancer is greater with high tar cigarettes than with medium tar cigarettes, it has not been clear whether the lung cancer risk continues to decline as tar levels decrease further.

To address this question, Harris et al analyzed the six-year mortality rate among smokers according to the tar content of brands smoked, most of which were low and medium tar cigarettes. No safety advantage with low tar cigarettes was found.

The study involved participants in the Cancer Prevention Study II. The population included 364,329 men and 576,535 women, all of whom were 30 or older in 1982. Of these, 100,868 men and 124,270 women were current smokers at study enrollment. The tar rating of the brands smoked and its relation to death from lung cancer was analyzed over a six-year period.

During this period, 2,622 men and 1,406 women died from cancer of the lung, trachea, or bronchus. Men and women who smoked either very low tar or low tar cigarettes had the same risk of lung cancer as did the smokers of medium tar brands. This observation persisted after adjusting for demographics, diet, occupation, and medical history. However, the lung cancer risk was even higher in those who smoked high tar cigarettes.

Harris et al found that smokers of low or very low tar cigarettes tended to smoke more cigarettes than did the other smokers, and they tended to inhale the smoke more deeply, thereby increasing the time the smoke was held in their lungs. Consequently, the actual dose of toxins to which these smokers were exposed may have been much higher than that predicted by machines designed to measure tar yields.

Harris JE, Thun MJ, Mondul AM, Calle EE. Cigarette tar yields in relation to mortality from lung cancer in the cancer prevention study II prospective cohort, 1982-8. BMJ. 2004;328:72-76.

POLYMORPHISM MAY PLAY A ROLE IN COPD

Although smoking is by far the biggest risk factor for COPD, studies have suggested that genetic factors may also be involved. Ito et al studied 103 COPD patients and 88 healthy smokers to determine the frequency of polymorphisms in the Gc-globulin gene. They found that patients with COPD have an increase in Gc*1F homozygotes.

Nine patients were classified as having stage I COPD, 38 had stage IIA, 37 had stage IIB, and 19 had stage III disease. Although there were no differences in allele frequencies between the patients with COPD and the controls, the COPD patients had an increased proportion of Gc*1F homozygotes.

The annual decline in FEV1 was calculated in 86 COPD patients and 21 controls. As a whole, the COPD patients had a significantly greater decline in lung function than did the controls. However, the COPD patients with Gc*1F alleles had a markedly greater decline in FEV1 than did the patients not having the allele. In addition, CT scans showed that severely emphysematous patients were more often in the group of Gc*1F+ patients than in those who were Gc*1F–.

The authors noted that although Gc*1F occurred more frequently among COPD patients than healthy smokers, the role of this genotype in the pathogenesis of COPD remains unclear.

Ito I, Nagai S, Hoshino Y, et al. Risk and severity of COPD is associated with the group-specific component of serum globulin 1F allele. Chest. 2004;125:63-70.

HYPOVENTILATION A DANGER IN SEVERELY OBESE PATIENTS

Hypoventilation is a consequence of severe obesity that frequently goes unrecognized and untreated. According to a study by Nowbar et al, who evaluated 150 severely obese patients, hypoventilation was associated with increased morbidity and mortality.

Patients were recruited from three hospitals during a six-month period. Hypoventilation was defined as a PaCO2 of 43 mm Hg or greater and a pH at or below 7.42. Arterial blood gas was obtained in 95% of patients when they were awake but supine.

Of the 150 patients, 47 (31%) met the criteria for obesity-related hypoventilation; the rest had simple obesity. The prevalence of obesity-related hypoventilation increased with body mass index (BMI): Hypoventilation was observed in 48% of patients with a BMI above 50 kg/m2. There was also a significant relationship between BMI and PaCO2 in both the patients with obesity-related hypoventilation and those with simple obesity.

Interestingly, there was no difference in discharge diagnoses between those with obesity-related hypoventilation and those with simple obesity. Although physicians were informed of patients who had hypercapnia and normal or low pH, only 11 patients received a discharge diagnosis of obesity-related hypoventilation. Furthermore, only six patients were discharged with a recommendation for long-term treatment. At 18 months, mortality was 23% among patients with obesity-related hypoventilation compared with 9% in those with simple obesity.

The authors suggested that arterial blood gas analysis be performed in all severely obese hospitalized patients—particularly those with daytime somnolence, headache, and dyspnea.

Nowbar S, Burkart KM, Gonzales R, et al. Obesity-associated hypoventilation in hospitalized patients: prevalence, effects, and outcome. Am J Med. 2004;116:1-7.

ICU MORTALITY LOW WHEN ACUTE RESPIRATORY FAILURE OCCURS ALONE

If acute respiratory failure (ARF) is not complicated by dysfunction of other organ systems, ICU survival is above 95%. However, more than 20% of patients die within 90 days of ARF onset, usually because of their underlying disease. When ARF is complicated by other types of organ dysfunction, both ICU and 90-day mortality rise markedly.

ARF is the most common type of organ failure in the ICU. Because most estimates of its mortality rate have included patients with other types of organ dysfunction, Flaatten et al studied 529 patients who were admitted to the ICU with ARF alone or who developed it while in the ICU. At admission, 137 patients had ARF alone and 255 had ARF plus one or more other types of organ failure. In addition, 19 patients developed ARF and 118 developed multiorgan failure while in the ICU.

The ICU, hospital, and 90-day mortality rates were lowest in patients with ARF alone; there was no difference in outcome between those who had ARF on admission and those who developed it in the ICU. Mortality increased sequentially with the number of additional organ failures. Overall, mortality at 90 days was 35.7% higher in the group with multiorgan failure than in the patients with ARF alone.

Of the 151 patients with single-organ ARF who survived their ICU stay, 29 had died by 90-day follow-up. These patients died of their underlying disease, not ARF.

Flaatten H, Gjerde S, Guttormsen AB, et al. Outcome after acute respiratory failure is more dependent on dysfunction in other vital organs than on the severity of the respiratory failure. Crit Care. 2003;7:R72-R77.

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