Distinguishing cubic and hexagonal phases within InGaN/GaN microstructures using electron energy loss spectroscopy.

3D InGaN/GaN microstructures grown by metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) have been extensively studied using a range of electron microscopy techniques. The growth of material by MBE has led to the growth of cubic GaN material. The changes in these crystal phases has been investigated by Electron Energy Loss Spectroscopy, where the variations in the fine structure of the N K-edge shows a clear difference allowing the mapping of the phases to take place. GaN layers grown for light emitting devices sometimes have cubic inclusions in the normally hexagonal wurtzite structures, which can influence the device electronic properties. Differences in the fine structure of the N K-edge between cubic and hexagonal material in electron energy loss spectra are used to map cubic and hexagonal regions in a GaN/InGaN microcolumnar device. The method of mapping is explained, and the factors limiting spatial resolution are discussed.

Nanoscale imaging of InN segregation and polymorphism in single vertically aligned InGaN/GaN multi quantum well nanorods by tip-enhanced Raman scattering.

Vertically aligned GaN nanorod arrays with nonpolar InGaN/GaN multi quantum wells (MQW) were grown by MOVPE on c-plane GaN-on-sapphire templates. The chemical and structural properties of single nanorods are optically investigated with a spatial resolution beyond the diffraction limit using tip-enhanced Raman spectroscopy (TERS). This enables the local mapping of variations in the chemical composition, charge distribution, and strain in the MQW region of the nanorods. Nanoscale fluctuations of the In content in the InGaN layer of a few percent can be identified and visualized with a lateral resolution below 35 nm. We obtain evidence for the presence of indium clustering and the formation of cubic inclusions in the wurtzite matrix near the QW layers. These results are directly confirmed by high-resolution TEM images, revealing the presence of stacking faults and different polymorphs close to the surface near the MQW region. The combination of TERS and HRTEM demonstrates the potential of this nanoscale near-field imaging technique, establishing TERS as a very potent, comprehensive, and nondestructive tool for the characterization and optimization of technologically relevant semiconductor nanostructures.

Continuous-flux MOVPE growth of position-controlled N-face GaN nanorods and embedded InGaN quantum wells.

We demonstrate the fabrication of N-face GaN nanorods by metal organic vapour phase epitaxy (MOVPE), using continuous-flux conditions. This is in contrast to other approaches reported so far, which have been based on growth modes far off the conventional growth regimes. For position control of nanorods an SiO(2) masking layer with a dense hole pattern on a c-plane sapphire substrate was used. Nanorods with InGaN/GaN heterostructures have been grown catalyst-free. High growth rates up to 25 microm h(-1) were observed and a well-adjusted carrier gas mixture between hydrogen and nitrogen enabled homogeneous nanorod diameters down to 220 nm with aspect ratios of approximately 8:1. The structural quality and defect progression within nanorods were determined by transmission electron microscopy (TEM). Different emission energies for InGaN quantum wells (QWs) could be assigned to different side facets by room temperature cathodoluminescence (CL) measurements.

[Eradication of measles in Cuba]. / La eliminación del sarampión en Cuba.

The vaccine against measles came into use in Cuba in 1971. During the seventies, a new early strategy for measles control was established, and it was followed by further efforts in the early eighties. Despite improvements to the control program, disease outbreaks continued to occur. In 1986, after examining the experience acquired through the control initiatives that were already in place, a new measles vaccination strategy was adopted. In time, the new vaccination strategy against measles came to have three main components: first, a single vaccination "catching-up" campaign targeting children 1 to 14 years of age. Second, efforts were made to achieve and maintain high vaccine coverage through mandatory vaccination services for 12-month-old children ("maintenance vaccination"). Finally, periodic "follow-up" campaigns were carried out for children 2 to 6 years of age. Steps were taken, for the purpose of monitoring the progress made so far toward eliminating measles, to strengthen disease surveillance systems, including the screening of suspected cases. The "catching-up" and "follow-up" campaigns both achieved greater than 98% coverage within targeted age groups. The routine vaccination program has also maintained high coverage. The high population immunity against measles that has been attained through these vaccination strategies has resulted in a rapid decrease in the incidence of the disease. From 1989 to 1992, less than 20 laboratory-confirmed cases were reported annually. In Cuba, the last case confirmed through serologic screening was reported in July 1993. Cuba's strategy for measles elimination has interrupted disease transmission and kept the causal virus from circulating on the island. Cuba's experience with measles elimination suggests that if an appropriate vaccination strategy is applied, measles can be globally eradicated.

Measles elimination in the Americas. Evolving strategies.

The strategy currently used to control measles in most countries has been to immunize each successive birth cohort through the routine health services delivery system. While measles vaccine coverage has increased markedly, significant measles outbreaks have continued to recur. During the past 5 years, experience in the Americas suggests that measles transmission has been interrupted in a number of countries (Cuba, Chile, and countries in the English-speaking Caribbean and successfully controlled in all remaining countries. Since 1991 these countries have implemented one-time "catch-up" vaccination campaigns (conducted during a short period, usually 1 week to 1 month, and targeting all children 9 months through 14 years of age, regardless of previous vaccination status or measles disease history). These campaigns have been followed by improvements in routine vaccination services and in surveillance systems, so that the progress of the measles elimination efforts can be sustained and monitored. Follow-up mass vaccination campaigns for children younger than 5 years are planned to take place every 3 to 5 years.

The epidemiology of measles.

Measles is a highly infectious disease which has a major impact on child survival, particularly in developing countries. The importance of understanding the epidemiology of this disease is underlined by its ability to change rapidly in the face of increasing immunization coverage. Much is still to be learned about its epidemiology and the best strategies for administering measles vaccines. However, it is clear that tremendous progress can be made in preventing death and disease from measles with existing knowledge about the disease, and by using the presently available vaccines and applying well-tried methods of treating cases. Research in the coming decade may provide more effective vaccines for use in immunization programmes. An understanding of the basic epidemiology of measles is a prerequisite for effective control measures.

PIP: The Expanded Programme on Immunization (EPI) dramatically increased coverage. In 1990, approximately 80% of the world's children younger than 1 year received measles vaccine, and it was estimated that around 2 million deaths were prevented. Still in 1990 an estimated 45 million cases and around 1 million deaths occurred in developing countries. In one community study in Kenya in 1985 measles accounted for 35% of reported deaths in infants 1-12 months old and for 40% of deaths in children 1-4 years old. The Schwarz vaccine was introduced in the 1960s; under most field conditions its efficacy is about 85% for children receiving the vaccine at 9 months or older. The urban poor, who usually have less access to immunization services, are usually the most at risk. Other high-risk groups include specific age groups (school children who represent cohorts from previous years when coverage was lower and who may not have been exposed to measles infection), ethnic minorities (who may have been underserved or may have rejected immunization for cultural reasons), hospitalized children who are at high risk of nosocomial transmission, and children in refugee camps. Vitamin A administered to children acutely ill with measles reduces mortality. Results from a trial in South Africa showed children treated with vitamin A had reduced risk of dying, recovered more quickly from pneumonia and diarrhea, and had less croup. In addition, symptomatic treatment for cases requires antibiotics to combat bacterial complications, and oral rehydration salts for dehydration following diarrhea. Case fatality rates can be lowered if cases reach health care facilities where appropriate care is offered early. For uncomplicated cases, supportive fluids, antipyretics, and nutritional therapy may be required. Many children need increased food intake for 4-8 weeks to recover their premeasles nutritional status.

A cluster of sternal wound infections requiring muscle flap repair: problems in epidemiologic investigation.

A cluster of sternal wound infections (SWI) requiring muscle flap closure occurred in a California hospital in 1988. Review of SWI rates by surgical team revealed that a single team (Team A) was associated with a cluster of SWI requiring muscle flap repair (MFR). Team A's rate of SWI requiring MFR was 2.27% in 441 heart operations. A case/control study was conducted to determine if the higher rate of SWI requiring MFR could be attributed to disproportionately large numbers of patients at high risk treated by Team A. Data on major risk factors for SWI collected for case and control groups included the following: age at operation, weight, body surface area, history of obesity, diabetes mellitus, or cigarette smoking, duration of cardiopulmonary bypass, use of internal mammary artery graft, number of coronary arteries bypassed, use of prostheses, operating room staffing, and emergent nature of operation. No statistically significant differences between Team A cases requiring MFR and control cases were observed for predisposing risk factors. Surgical technique remains a principal suspected risk factor for SWI requiring MFR in this cluster.

[White sponge nevus]. / Naevus spongiosus albus mcuosae (Weisser Schwammnaevus).

White sponge nevus is a rare disturbance of the keratinization of the oral mucosa. Differential diagnosis and therapy are discussed on the basis of one case with typical clinical and histologic findings.

[Incidence of bacteremia following extractions--a double blind study on local disinfection using chlorhexidine]. / Bakteriämie-Häufigkeit bei Extraktionen. Doppelblindstudie zur lokalen Desinfektion mit Chlorhexidin.

In a randomised double-blind study the incidence of bacteremia after two minutes mouth rinsing with chlorhexidine 0.1% followed by tooth extractions was registered. A significant reduction of bacteremia could not be observed in comparison with mouth rinsing with physiological saline solution. Tooth extractions always require the preventive administration of antibiotics to patients known with high risk of endocarditis.

Improving disease reporting in Los Angeles County: trial and results.

A telephone survey of physicians in Los Angeles County revealed that 50 percent of 405 contacted were unaware of the legal mechanism for reporting communicable diseases--the Confidential Morbidity Report (CMR) card. After that survey, three measures were taken in an effort to improve reporting and surveillance: (a) use of a stamped self-addressed CMR postcard, (b) publication of the monthly newsletter "Public Health Letter," which was distributed to 23,000 health professionals in Los Angeles County free of charge, and (c) initiation of an active disease surveillance system that included 171 reporting sites contacted weekly (76 physicians, 36 schools, 33 preschools, 22 hospitals, and 4 university student health centers). No increase in the levels of disease reporting was observed, based on 4 years' experience with the revised CMR card and the Public Health Letter. The active disease surveillance system, however, has provided anecdotal reports of disease occurrence and notification of outbreaks of both reportable and nonreportable diseases. Moreover, the authors believe it has improved rapport between the county health department and the medical community.

Amebic infections in asymptomatic homosexual men, lack of evidence of invasive disease.

A survey for enteric infections in 140 asymptomatic homosexual men who attended a community clinic revealed a high prevalence of infection with Entamoeba histolytica (27.1 per cent) and Giardia lamblia (15.7 per cent). In contrast, the prevalence of elevated indirect hemagglutination (IHA) titers (greater than or equal to 1:128), which indicate invasive amebiasis, was low (5.7 per cent). Our findings suggest that only a limited amount of invasive amebic disease is occurring in this group of homosexual men.

Influenza in the elderly: report of an outbreak and a review of vaccine effectiveness reports.

An outbreak of influenza A in nursing home residents is reported and other studies of influenza vaccine effectiveness in elderly populations are reviewed. The outbreak occurred in a Los Angeles nursing home between February and March 1983. Of the 87 residents, 46 (53%) were affected with influenza-like illness. Attack rates were similar between immunized and unimmunized residents (52% versus 58%), and yielded a vaccine effectiveness estimate of 10%. No additional protection could be demonstrated in residents who received vaccine for two consecutive years. Seven persons died (mortality rate of 8.1%); the mortality rate was greater in the unimmunized (15.8%) than in the immunized (6.2%). Because this study and other field studies of influenza vaccine are limited in precision and power, a statistical summary of the various studies was constructed. Summarizing the studies of institutionalized elderly (in hospitals and nursing and retirement homes) yielded an estimate of 74% for the average vaccine effectiveness in mortality reduction, and an estimate of 33% for the average effectiveness in preventing clinical illness. For the non-institutionalized elderly, the corresponding estimates were 47% for mortality, and 5% for clinical illness. Despite the obvious limitations of such summaries, it seems reasonable to conclude that influenza vaccines have on the average been of clear benefit in the institutionalized elderly, while the benefits in the non-institutionalized elderly have been less dramatic and may warrant further investigation.

Clinical effectiveness of rubella vaccine in a college population.

An outbreak of rash-like illness compatible with rubella occurred among the student population of a large university in Los Angeles between November 1, 1981 and January 31, 1982. A case-control study was conducted in order to estimate the effectiveness of rubella vaccine in preventing clinical rubella in this university population. Immunization and disease histories were obtained from parents and physicians for 39 cases and 86 controls. For those students with a clear documentation of immunization history, only one of 16 cases (6%) had evidence of prior rubella immunization, compared with 40 of 56 controls (71%). This yielded an estimated vaccine effectiveness of 97% (95% confidence limits of 82% to 100%). The level of protection observed for students immunized with rubella vaccine in our study population was high and comparable to that reported in other recent studies. This supports the notion that the current large reservoir of young adult susceptibles is primarily attributable to past failures to vaccinate school-age children, rather than vaccine failures.

An outbreak of respiratory syncytial virus pneumonia in a nursing home for the elderly.

An outbreak of pneumonia and febrile respiratory illness took place in a Los Angeles County nursing home for the elderly in February and March of 1979. Forty of 101 (40%) residents were affected. Twenty-two (55%) had pneumonia and eight (20%) died. The outbreak extended over a period of 6 weeks. Serological evidence implicated respiratory syncytial virus (RSV) as the causative agent. Three patients had fourfold or greater rises in the titre of antibody to RSV, one had high titres in paired samples of serum, while nine had a titre of greater than or equal to 64 in a single convalescent sample. RSV may be a more important cause of lower respiratory illness among the elderly in residential institutions than previously recognised.

Rubella in hospital employees.

In early 1982, 15 hospitals in Los Angeles County reported one or more serologically confirmed rubella cases among their employees. Secondary cases occurred at eight hospitals; overall, 56 cases were identified among employees, of which 28 were serologically confirmed. Testing of 2,061 employees revealed 1,770 (86%) with detectable antibody. A survey of 83 hospitals offering obstetrical services indicated only 42% (33 of 78) had an established rubella screening policy. Based on the results of this survey, the Los Angeles County Department of Health Services published recommendations for hospital rubella screening and immunization policies.

A population-based case-control study of anencephalus and spina bifida in a low-risk area.

For the period 1973 to 1977, a total of 536 cases of anencephalus and spina bifida were ascertained in Los Angeles County, California, a low-risk area, and compared with a 2 per cent random sample of all live births in the county. Women with Spanish surnames had an elevated risk for anencephalus and to a lesser extent for spina bifida; Blacks were at lowest risk, especially for spina bifida. The occurrence of a previous fetal death was a strong risk factor for anencephalus but there was no association between socio-economic status and either of the defects. Advanced maternal age was a stronger risk factor for spina bifida than for anencephalus but, as in other studies in low-risk areas, no increased risk was observed among teenage mothers. Paternal age did not show any independent association after controlling for mother's age. Finally, the association of high birth-order with the birth defects was weakened greatly after simultaneous adjustment for age and ethnicity.