The effect of random vaccine response on the vaccination coverage required to prevent epidemics

The response people have to vaccination varies because their immune systems differ and vaccine failures occur. Here we consider the effect that a random response, independent for each vaccinee, has on the vaccination coverage required to prevent epidemics in a large community. For a community of uniformly mixing individuals an explicit expression is found for the critical vaccination coverage (CVC) and the effect of the vaccine response is determined entirely by the mean E(AB), where A and B, respectively, reflect the infectivity and susceptibility of a vaccinated individual. This result shows that the usual concept of vaccine efficacy, which focuses on the amount of protection the vaccine provides the vaccinee against infection, is not adequate to describe the requirements for preventing epidemics when vaccination affect infectivity. The estimation of E(AB) poses a problem because A and B refer to the vaccine response of the same individual. Similar results are found when there are different types of individual, but now the mean E(AB) may differ between types. However, for a community made up of households it is shown that the CVC also depends on other characteristics of the vaccine response distribution. In practice this means that estimating a single measure of vaccine effectiveness is generally not enough to determine the CVC. For a specific community of households it is found that the vaccination coverage required to prevent epidemics decreases as the variation in the vaccine response increases.     

Risk stratification using the Society of Thoracic Surgeons Program

In an era of progressive cost containment and public scrutiny, the wisdom of aggressive surgical therapy for high-risk candidates has been questioned. At our center in the previous 24 months, 728 patients with coronary artery disease were entered into The Society of Thoracic Surgeons national database, and the hospital outcomes plus length of stay were analyzed. Patients were separated according to the predicted mortality based on the groupings in The Society of Thoracic Surgeons database: 0 to 5% (453 patients); 5% to 10% (126 patients); 10% to 20% (96 patients); 20% to 30% (17 patients); and 30% and greater (36 patients). There was a close correlation with the predicted rates of mortality. Importantly, the preoperative risk stratification demonstrated a strong correlation with the significant morbidity and excessive length of stay in the highest-risk groups (predicted risk of 20% to > or = 30%). The incidences of the most common complications in the group with the highest predicted risk (> or = 30%) were 28%, renal failure; 33%, ventilator dependence; and 17%, cardiac arrest. In addition, at short-term follow-up (6 to 8 months), a 24.3% mortality was identified in patients with a predicted mortality that exceeded 20%. These data quantify the risks and morbidities associated with the care of seriously ill patients with coronary artery disease and demonstrate the need for professional and public discussions focusing on the association of a high preoperative risk status and the consumption of resources.     

Learning curve for oesophageal cancer surgery

BACKGROUND: Surgical training and experience are frequently claimed to influence early and late outcome measures. The aim of this study was to examine any improvement in an individual surgeon's performance in one operation over a period of 7 years from initial appointment to date. METHODS: Patients undergoing Ivor Lewis subtotal oesophagectomy performed by a single surgeon between April 1990 and December 1996 were identified from a prospectively compiled oesophageal cancer database. Operating time (abdominal, thoracic and 'one-lung time'), blood loss, transfusion requirements (intraoperative and total), extent of lymphadenectomy (number of lymph nodes sampled), intensive treatment unit (ITU) stay, hospital stay, postoperative morbidity and mortality, pathological stage, grade and survival were recorded. RESULTS: The records of 150 patients were identified for analysis. The cohort was split into five groups, each of 30 patients operated on consecutively. Each of the groups was comparable for age, sex, smoking history, preoperative haemoglobin and creatinine levels, weight loss, American Society of Anesthesiologists' grade, and histological stage and grade of disease. Analysis of the variables pertaining to operation revealed a significant improvement with time including reduced single-lung operating time (P=0.01), reduced blood loss (P=0.03), reduced transfusion requirement (P < 0.0001), reduced ITU stay (P< 0.0001), reduced inpatient stay (P< 0.0001) and an increased yield of lymph nodes (P < 0.0001). CONCLUSION: This study showed a continuing improvement in a surgeon's performance over a 7-year period. With the current trend to shorter training periods there is a case for continuing supervision of the 'fully trained' surgeon within highly specialist units.     

Genetic basis of neurological tumours

Neurological tumours are common neoplasms of both adults and children. Recent studies have begun to delineate the genetic abnormalities that underlie such tumours, and have implicated two classes of genes, oncogenes and tumour suppressor genes. Most investigations have focused on those astrocytomas that affect the cerebral hemispheres of adults, since these are the most common and malignant brain tumours. The high-grade astrocytomas that affect adults, such as glioblastoma multiforme, often have amplification of the epidermal growth factor receptor (EGFR) oncogene and loss of a variety of chromosomal loci that probably harbour tumour suppressor genes. Of the various tumour suppressor gene loci, the p53 gene on chromosome 17p has been studied most closely and has been shown to be mutated in both low- and high-grade astrocytomas. These genetic alterations may provide a means for subdividing astrocytomas into diagnostic categories. For instance, p53 gene mutations occur more commonly in glioblastomas from young adults and women, while EGFR gene amplification is more common in glioblastomas from older adults and men. For the other primary CNS tumours, genetic studies remain in their infancy. The neurocutaneous syndromes, such as neurofibromatosis types 1 and 2, have provided unique insights into neurological oncogenesis. The NF1 gene on chromosomes 17q and its product, neurofibromin, may be important in the formation of neurofibrosarcomas, while the NF2 gene on chromosome 22q and its product, merlin, are probably involved in the formation of schwannomas and other nervous system tumours. The further characterization of these and other neurological tumour genes will undoubtedly illuminate many other areas in neurooncology.     

The Employee Health Care Value Survey: round one

In a groundbreaking arrangement, a consortium of large employers--the Xerox, GTE, and Digital Equipment Corporations--launched the Employee Health Care Value Survey during fall 1993. Completed by 24,306 employees, this survey was used to develop comparable methods for assessing corporate health care benefit strategies. It also enabled fair comparisons of thirty-two health plans across the country on more than sixty criteria. Variation in performance among plans was substantial, with managed care plans--particularly prepaid group practices and individual practice associations (IPAs)--recording the most favorable rankings on disenrollment, overall satisfaction, and other measures of "bottom-line performance." Variation in enrollees' health among plans was more modest, with indemnity enrollees posing a somewhat greater illness burden to their plans than enrollees of other plan types. The employers and evaluated health plans are now using the results for multiple purposes, including quality improvement initiatives, employee-based plan performance reports, employee contribution strategies, and health promotion programs.     

The formation of cardiac-electric-field potentials on the surface of the heart and torso in vertebrate animals

The comparative electrophysiological study of excitation process in heart with different types of organization have laid the foundation for solution of the problems of formation of cardioelectric field. It was shown, that the form of extracellular potentials on the epicardium correlated with different types of ventricle myocardial activation. Animals with the "flash" type of myocardial depolarization in most cases have the negative extracellular potentials in the greater part of the epicardial ventricular surface. Animals with the consecutive type of myocardial activation--the positive and biphase potentials. All myocardial layers (epicardial, intramural and endocardial) are electrophysiologically informative.     

The psychocultural roots of genocide. Legitimacy and crisis in Rwanda

In April 1994, the small east African nation of Rwanda became the site of one of the most violent episodes of the 20th century. Over the course of just 100 days, an embattled authoritarian state organized the slaughter of at least 850,000 Rwandans. Briefly, worldwide attention was riveted. But clichés about "age-old tribal hatreds" soon dominated discussion, conveying the impression that this was simply the latest episode in an unending cycle of violence. The truth, however, is quite different. The April genocide was in many ways unique. It was neither tribal nor age-old, and it is hardly fated to recur. Indeed, the author's premise is that if this genocide is grasped in all its psychocultural novelty and complexity, a point of Archimedean leverage can be found for interventions to avert tragedies in the future.     

Treatment of acute bronchitis in adults without underlying lung disease

OBJECTIVE: To determine whether antibiotic and bronchodilator treatment of acute bronchitis in patients without lung disease is efficacious. DESIGN: A MEDLINE search of the literature from 1966 to 1995 was done, using "Bronchitis" as the key word. Papers addressing acute bronchitis in adults were used as well as several citations emphasizing pediatric infections. A manual search of papers addressing the microorganisms causing acute bronchitis was also done. Data were extracted manually from relevant publications. SETTING: All published reports were reviewed. Papers dealing with exacerbations of chronic bronchitis were excluded in this review. RESULTS: Although acute bronchitis has multiple causes, the large majority of cases are of viral etiology. Mycoplasma pneumoniae, Chlamydia pneumoniae, and Bordetella pertussis are the only bacteria identified as contributing to the cause of acute bronchitis in otherwise healthy adults. Nine double-blind, placebo-controlled trials were reviewed. Four studies showed no advantage for doxycycline and one study showed no advantage for erythromycin. One study using erythromycin and one study using trimethoprim and sulfamethoxazole showed that these antibiotics were slightly better than placebo. Two other studies showed an impressive superiority for liquid or inhaled albuterol when compared with erythromycin. CONCLUSIONS: Most studies showed no significant difference between drug and placebo, and the two studies that did showed only small clinical differences. Albuterol had an impressive advantage over erythromycin. Antibiotics should not be used in the treatment of acute bronchitis in healthy persons unless convincing evidence of a bacterial infection is present.     

A note on formal learning theory

Previous investigations have challenged the generality of the claim that perceived motion in an effective stimulus for smooth pursuit eye movements. The experiments extend the scope of these investigations. Three experiments test the hypothesis that perceived motion can serve as the stimulus for pursuit when the eye movement does not generate constraining retinal error information. Observers viewed retinally stabilized displays that elicited the perception that a stationary target was moving or that a moving target was moving faster than it was actually moving. The results failed to confirm the hypothesis. Relevant literature is reviewed. We conclude that perceived movement can act as a stimulus for pursuit only when the "perceptual target" has no retinal counterpart.