An operational research approach to estimating the age distribution of residence time in an HIV/AIDS core group.

An operational research approach is used to estimate the age distribution of residence time in an HIV/AIDS core group of gay men, employing only good public health data for administration, planning and decision-making. Any HIV/AIDS modelling involving a high-activity high-risk core group must allow for a restricted but variable residence time in the group. An earlier steady-state approximation by Bailey assumed an arrival process with negligible departures, followed by a departure process with negligible arrivals. That conjecture naturally overestimated the average residence time. An improved model, using age-dependent public health data on AIDS for some 4129 cases in gay men in San Francisco, has now been reanalysed to present the distribution of age at a fixed point of time close to the peak of the underlying HIV epidemic. It is important to note that these data, at any rate, have no appreciable age-dependence in the observed incubation periods. We have adopted the underlying infection dynamics of Jacquez et al. that recognizes an initial concentrated period of high infectivity in all HIV positives leading to a well-marked primary HIV epidemic. Maximum-likelihood estimation has been used to identify five major parameters with small standard errors. The residence model as a whole gives a good fit to the reanalysed data with chi(2)(4)=2.83.

Coronary revascularization in heart transplant recipients by excimer laser angioplasty.

BACKGROUND AND OBJECTIVE: Aggressive development of allograft coronary artery disease is a major cause of death in heart transplant recipients. Percutaneous balloon angioplasty is considered suboptimal for complex lesions in native coronary vessels and heart transplant recipients, alike. Excimer laser energy (308-nm wavelength) can successfully remove and vaporize atherosclerotic plaques in native coronary vessels; however, its application in heart transplant recipients has not been studied clinically yet. STUDY DESIGN/MATERIALS AND METHODS: Six heart transplant recipients underwent percutaneous excimer laser (CVX-300, Spectranetics, Colorado Springs, CO) coronary angioplasty for treatment of a total of 10 discrete, obstructive coronary artery lesions. By using concentric or eccentric multifiber laser catheters, energy parameters were set at a fluence of 45 mJ/mm(2) or 60 mJ/mm(2) with a frequency of 25 Hz and 40 Hz, respectively, with a pulse duration of 135 ns and output of 200 mJ/pulse. The "saline flush" and "pulse and retreat" lasing techniques were used. In each case, adjunct balloon angioplasty was performed; in five lesions, an intracoronary stent was implanted. Angiographic evaluation was performed by visual assessment. RESULTS: Each procedure was successful as defined by laser recanalization of the target lesion (reduction of target lesion stenosis in more than 20%) and subsequent adequate final luminal patency (reduction of target lesion stenosis to less than 50%) and absence of any major in-cardiac catheterization complication (such as perforation, acute closure, dissection, emergency coronary artery bypass surgery), or in-hospital complications (such as death, myocardial infarction, cardiac enzyme elevation, major bleeding), or need for surgical revascularization. A 92 +/- 5% preprocedural percent diameter stenosis was reduced by laser to 35 +/- 16% and by adjunct balloon angioplasty in all lesions and stenting in five lesions, to final residual stenosis of 2 +/- 6%. Angiographic follow-up between 2 and 6 months after the procedure demonstrated a target lesion restenosis rate of 22%. CONCLUSION: Percutaneous excimer laser is safe and efficacious in the treatment of focal obstructive lesions caused by allograft coronary artery disease. These data represent an early clinical experience; thus, the long-term outcome of this revascularization method in recipients of heart transplantation will have to be determined by a large scale prospective, randomized, multicenter clinical study.

Application of solid-state pulsed-wave, mid-infrared laser for percutaneous revascularization in heart transplant recipients.

BACKGROUND: Severe allograft coronary artery disease is a significant cause of death in heart transplant recipients. Percutaneous revascularization has thus far been attempted with balloon angioplasty and, to a lesser extent, with directional atherectomy. The new, investigational, solid-state pulsed-wave mid-infrared laser (holmium:YAG) can vaporize and remove atheromatous and thrombotic plaques. This mechanism of plaque ablation may be useful for allograft coronary artery disease associated with focal stenoses deemed unsuitable for standard balloon angioplasty, especially thrombus-containing lesions. METHODS: Five adult heart transplant recipients with severe focal stenoses related to allograft coronary artery disease underwent six laser angioplasty procedures. Laser catheters (2.1 microm, 250 to 600 mJ, 5 Hz) varying from 1.2 mm to 2.0 mm delivered 45 +/- 7.4 pulses (mean +/- SD). Five laser procedures were completed with adjunct balloon angioplasty and one with directional atherectomy. RESULTS: Laser success (defined as stenosis reduction > 20%, no cardiac catheterization laboratory or in-hospital major complication) was achieved in six of seven lesions (85%), and the overall (laser and adjunct balloon) procedural success rate was 100%. No major complications occurred. Laser-assisted angioplasty reduced mean stenosis from 90% +/- 3% to 9% +/- 11%. All five patients recovered and were discharged. Angiographic follow-up demonstrated a 50% restenosis rate. CONCLUSIONS: In selected heart transplant recipients laser-assisted angioplasty can provide safe and successful acute revascularization. Focal lesions considered "nonideal" for balloon angioplasty and, in particular, thrombotic lesions can benefit from application of this device; however, long-term reduction of restenosis rates is not expected from this modality.

A revised assessment of the HIV/AIDS incubation period, assuming a very short early period of high infectivity and using only San Francisco public health data on prevalence and incidence.

A revised assessment of the HIV/AIDS incubation period has been made, based on an updated operational model that includes a very short early period of high infectivity, following recent work by Jacquez et al. and using AIDS incidence data from the San Francisco Department of Public Health, plus data on AIDS incidence and HIV prevalence in a specially recruited cohort from the San Francisco City Clinic. The incubation period has, approximately, a suitably scaled gamma distribution with 14 degrees of freedom and mean 12.8 (SE 0.2) years. This information is essential in interpreting data from other areas and regions where AIDS incidence figures only are available, and is in particular intended for applications to several countries in Europe.

Anatomic variant of the posterior interventricular coronary artery: implications for coronary angioplasty in acute myocardial infarction.

Acute thrombotic occlusion of an infarct-related artery is frequently found in patients presenting with myocardial infarction. In a patient with acute inferior wall myocardial infarction complicated by continuous chest pain and hemodynamic instability, emergency diagnostic coronary arteriography demonstrated a patent, infarct-related, "pseudo" right coronary artery while, in fact, this vessel was a rare anatomic variant of the posterior interventricular branch with very early origin from the right coronary artery and the true right coronary artery was completely occluded by a thrombotic obstruction. Accurate anatomic-angiographic interpretation of the angiogram was crucial for successful performance of emergency recanalization and revascularization of the true right coronary artery with laser and balloon angioplasty. Once antegrade flow was restored another rare coronary variant was discovered, i.e., a sinoatrial node artery arising from the middle portion of the newly patent right coronary artery.

Prediction and validation in the public health modelling of HIV/AIDS.

Mathematical models are an integral part of long-range scientific research and are broadly equivalent to the hypotheses to be tested. Validation consists: (1) in checking whether theoretical expectations are sufficiently close to observed values; and (2) in showing that theoretical constructions that pass the first test can also make verifiable predictions of future events. When modelling is used in operational situations to assist practical decision-making, as in the public health surveillance, prediction and control of infectious diseases, especially HIV/AIDS, it is easy to use the first criterion, but not so simple to implement the second. The paper discusses various methods of improving the validation of a specific classical compartmental model of HIV/AIDS geared to good serial public health data on AIDS incidence. These methods include model fitting to existing data, cross-checking findings with independent research results, general circumstantial support, and the possibility in special situations of the quasi-prediction of present or recent data using models fitted only to sufficiently distant past data.

An improved hybrid HIV/AIDS model geared to specific public health data and decision making.

An improved version of a previously described compartmental dynamic model for the spread of the HIV virus and AIDS is presented in which the estimation of key parameters depends entirely on the use of good public health data. This means that practical applications to specific regions, using only local data, can be of great value to public health decision makers dealing with local problems. It is assumed that scientific support is available within an interdisciplinary operations research context. The improved model incorporates physicians' delays in reporting AIDS incidence, additional cases revealed by death certificate analysis, and a high-risk core group of HIV positives involving a limited residence time, followed by a low-risk group with extended residence, both groups leading to AIDS cases. The model is hybrid in character in the sense that the HIV infection process with large numbers is deterministic while the incubation process with small numbers initially is stochastic. Applications have been made to Switzerland. Key parameters estimated include, in particular, the actual sizes of the original core groups for gay men and intravenous drug users. Current numbers of circulating HIV positives are also obtained.

The use of operational modeling of HIV/AIDS in a systems approach to public health decision making.

Compartmental models of infectious diseases readily represent known biological and epidemiological processes, are easily understood in flow-chart form by administrators, are simple to adjust to new information, and lend themselves to routine statistical analysis such as parameter estimation and model fitting. Technical results are immediately interpretable in epidemiological and public health terms. Deterministic models are easily stochasticized where this is important for practical purposes. With HIV/AIDS, serial data on both HIV prevalence and AIDS morbidity have been available from San Francisco. Assuming the distribution of the incubation period to be biologically stable, statistical analysis is quite feasible in other regions, even those with no reliable HIV data. Transmission rates must be estimated locally. It is also often possible to estimate the effective size of a population subgroup at risk, from population data on AIDS morbidity only. Computer simulation provides estimates of the evolving pattern of both HIV prevalence and AIDS morbidity. Some public health questions can be answered only by appropriately formulated stochastic models.

The case for mathematical modelling of schistosomiasis.

Large problems, such as the large-scale transmission of parasitic disease, are complex and difficult to predict. Understanding them, in order to make cost-efficient choices about possible control interventions, requires knowledge from a very wide range of specialists. Modelling the system can help to do this, but must not ignore the specific requirements of administrators and executives who have to work with high-level decisions about disease control. To many, the modelling approach seems arcane and divorced from reality, unable to answer the decision-makers. But techniques are improving, and in this article, Norman Bailey puts the case for the mathematical modelling of schistosomiasis.

The structural simplification of an epidemiological compartment model.

It is shown how a multicompartmental infectious disease model can be systematically examined for reduction of structural complexity. For steadystate situations, four basic rules are proposed for eliminating components of flow-lines, whole flow-lines, and compartments, plus combining compartments. An application to a typhoid fever model allows calculations to be done on a pocket calculator. The approach could be particularly important in developing countries.

Introduction to the modelling of venereal disease.

The continually rising trend in the incidence of venereal diseases, especially gonorrhoea, in a large number of countries, both developed and developing is causing considerable public health concern. There is a disquieting volume of human suffering involved, as well as large economic losses in treatment and hospitalization. The present paper reviews the existing state of development in the mathematical modelling of the relevant disease dynamics. The 'criss-cross' nature of the infections, which in heterosexual contacts switch between the male and female populations, together with the nonlinear form of the rate of spread normally occurring in infectious diseases, leads to special types of simultaneous nonlinear differential equations.