Farr's law applied to AIDS projections.

Farr's Law of Epidemics, first promulgated in 1840 and resurrected by Brownlee in the early 1900s, states that epidemics tend to rise and fall in a roughly symmetrical pattern that can be approximated by a normal bell-shaped curve. We applied this simple law to the reported annual incidence of cases of acquired immunodeficiency syndrome in the United States from 1982 through 1987. The 6 years of incidence data closely fit a normal distribution that crests in late 1988 and then declines to a low point by the mid-1990s. The projected size of the epidemic falls in the range of 200 000 cases. A continuing incidence of endemic cases can be expected to emerge, but we believe it will occur at a low level.

An epidemiologic and clinical evaluation of Guillain-Barré syndrome reported in association with the administration of swine influenza vaccines.

As a result of a court order, computerized summaries of approximately 1,300 cases reported as Guillain-Barré syndrome by state health departments to the Centers for Disease Control during the intensive national surveillance instituted following the swine influenza vaccination program in 1976-1977 became available for further study. Although the data were not uniformly adequate to confirm the diagnosis of Guillain-Barré syndrome, they were sufficient to enable classification according to extent of motor involvement. Vaccinated cases with "extensive" paresis or paralysis occurred in a characteristic epidemiologic pattern closely approximated by a lognormal curve, suggesting a causal relationship between the disease and the vaccine. Cases with "limited" motor involvement showed no such pattern, suggesting that this group included a substantial proportion of cases which were unrelated to the vaccine. The effect attributed to the vaccine lasted for at least six weeks and possibly for eight weeks but not longer. The relative risk of acquiring "extensive" disease over a six-week period following vaccination ranged from 3.96 to 7.75 depending on the particular baseline estimate of expected normal or endemic incidence that was chosen. Correspondingly, the number of cases that could be attributed to the vaccine over the six-week period ranged from 211 to 246, or very slightly higher over an eight-week period if the lowest baseline estimate was used. The total rate of Guillain-Barré syndrome cases attributed to prior use of the vaccine was 4.9 to 5.9 per million vaccinees.

Oral rehydration in diarrhoea : applied pathophysiology.

The main danger of acute diarrhoea is the loss of body water and electrolytes. The scientific rationale for oral rehydration therapy depends on the function of the small bowel enterocytes. Recent studies have indicated that active secretion rather than a failure of absorption is the main mechanism for most cases of acute disease. The linked-absorption process of sodium and substrate enhance the assimmlation of replacement fluid and remains intact in most cases of diarrhoea. A suitable rehydration mixture depends on: the physiology of the absorption mechanism, the chemical composition of fluid secreted in the particular type of diarrhoea, and on practical factors relating to the cost and availability of ingredients. Oral rehydration therapy is an appropriate primary health care technique for use in early acute diarrhoea.

The epidemiology of influenza.

Although unpredictable, influenza outbreaks are known to occur in three patterns: pandemics every 30 to 40 years, with high excess mortality; epidemics much more frequently, with lower excess mortality; and usually mild sporadic outbreaks. The possibility of a swine-flu pandemic this winter, resembling that of 1918-20, is the result of a unique deviation in the epidemiology of this fascinating disease.

William Farr: founder of modern concepts of surveillance.

Considerable confusion surrounds the use of the term surveillance in the context of public health but the principles underlying all uses are as old as epidemiology itself. William Farr has contributed more than anyone else to the development of these principles and to the demonstration of their value in practice on a large scale. This paper re-examines the basic tenets which guided him and the methods and techniques which he developed in the hope of reviving insights and resetting standards that modern epidemiologists might, with benefit, strive to emulate.

The use of the 'blind' problem in teaching epidemiology.

In the use of the case-study or problem-solving method of teaching epidemiology, the technique of the 'blind' problem, namely the withholding of the diagnosis of the disease until the end, presents many advantages. The student is forced to confront the purely epidemiological data without being prejudiced by his preconceived notions about the disease in question. In the study of an individual clinical case the objective is to make a diagnosis so that an accurate prognosis and specific treatment may be determined. So, in the study of an epidemic or outbreak (an epidemiological case) the objective is to establish a source of infection, a mode of spread or an aetiological factor, in order to predict a future trend and institute specific control measures. The 'blind' problem creates suspense, enhances the intellectual challenge, and permits the student and discussion leader to test a variety of hypotheses purely on the basis of the epidemiological evidence presented. An example of a localized epidemic is presented to illustrate these points.