Targeted screening of high-risk cattle populations for BSE to augment mandatory reporting of clinical suspects.

In Switzerland, the first case of bovine spongiform encephalopathy (BSE) was diagnosed in November 1990. Case numbers peaked in 1995, with a total of 352 BSE cases identified by 30 April 2000. Reporting of clinically suspect cattle is currently the most commonly used method world-wide to detect BSE cases. The effectiveness of mandatory reporting depends on a variety of factors; for other diseases passive surveillance underestimates the incidence of clinical cases. The efficiency of passive surveillance systems for BSE will remain unknown until screening tests able to identify clinically affected cattle have been applied in several countries. This paper provides the first detailed description of a targeted screening programme for BSE. Two populations of cows >24 months of age were included in the targeted screening: (i) cows found dead or culled on site where the carcass was submitted to rendering (fallen stock) and (ii) cows with health-related problems unfit for routine slaughter that were slaughtered under emergency procedures (emergency slaughter). Between 1992 and 1999, on average 81 clinical BSE suspects per year were reported to the veterinary authorities (passive surveillance), of which 43% were confirmed with BSE. A total of 30 clinical cases were captured by passive surveillance and an additional 20 BSE cases detected by targeted screening between May 1999 and April 2000. The odds of finding a BSE case was 49 times higher in the fallen stock and 58 times higher in emergency-slaughtered cattle when compared to passive surveillance. The targeted screening of fallen stock and emergency-slaughtered cattle considerably increased the number of detected cases in this 12-month period. Targeted-screening cases were on average 4 months younger than the clinical suspect cases. In conclusion, post-mortem testing of fallen stock and emergency-slaughtered cows >24 months for BSE is an important active surveillance element within a total surveillance system that principally is based on mandatory reporting of clinical suspect cases. Without ante-mortem screening tests to detect BSE-infected cattle during the incubation period, a combination of effectively functioning passive and active BSE surveillance strategies might be the only approach to assess the BSE situation reliably in a given country or region - and it is necessary to substantiate claims of freedom from the disease.

Does improvement in case ascertainment explain the increase in sporadic Creutzfeldt-Jakob disease since 1970 in the United Kingdom?

The aim of this study was to quantify the improvements in case ascertainment which are considered to explain the rise in the incidence of sporadic Creutzfeldt-Jakob disease. The numbers of cases, falling into five 10-year age groups starting at the age of 30 and three calendar periods of report since 1970, were analyzed by Poisson regression, assuming a constant age distribution. The age-period and age-cohort models were applied and discussed. The age-period model showed that underreporting in 1970-1979 was greater among patients aged 70 years or older. The age-cohort model indicated that a cohort factor increased over the first half of the 20th century (e.g., the incidence in the generation born in 1940 was almost twice that in the generation born in 1920); this increase was probably an artifact due to the past underascertainment pattern. However, from a statistical viewpoint, both models lead to a good fit; the cohort factor may appear to be as relevant as the period factor in describing the trends in incidence. Thus, one can imagine an unlikely worst case scenario, assuming that an unknown cohort factor is involved. In that case, the age-cohort model gives more optimistic predictions than Neilson's model (BMJ 1996;312:1038-9). These results are consistent with both interpretations: The rise in incidence is governed by improvements in case ascertainment, and is greater among old people (the most accepted interpretation); this rise may depend on a cohort factor as well, which may correspond to the zoonotic hypothesis (a totally hypothetical interpretation). Interpreting the increase of sporadic Creutzfeldt-Jakob disease over generations in terms of exposure to putative environmental factors is still a matter of debate; ongoing epidemiologic surveys may provide more information. Presently, this increase can be explained as an artifact due to the past underreporting pattern, with 79% (95% confidence interval: 56, 90) of the cases among persons aged > or =70 years being missed in 1970-1979.

When did bovine spongiform encephalopathy (BSE) start? Implications on the prediction of a new variant of Creutzfeldt-Jakob disease (nvCJD) epidemic.

BACKGROUND: Knowing the starting date of the BSE epidemic and its size at the very beginning is crucial to interpret the timing of the nvCJD cases and to forecast the nvCJD epidemic. The first cases occurred in 1985. The models devised by Anderson (back-calculation) and Dealler (age-period-cohort) led to an estimate of less than 50 cases in 1983, and none earlier. Here, we applied age-cohort models to the BSE data in order to estimate the earliest possible date of the first unrecognized BSE cases. METHODS: The numbers of confirmed BSE cases in the UK, by age group and by calendar year from 1988 to 1996, were analysed by Poisson regression. The cases' age distribution was considered as constant between the different birth cohorts. The herd's age structure was taken into account. RESULTS: According to the models, BSE cases may have occurred as early as 1980. The expected number of cases before 1990 is almost twice the number of confirmed cases and exceeds by more than 20% the expected value of Anderson's model. The scenario of first human exposure in 1980 leads to fewer future nvCJD cases than predicted by Cousens with exposure patterns starting in 1983 or 1985. CONCLUSION: The first birth cohort available, consisting of two cases older than 10 in 1988, does not allow any projections before 1980. Moreover, confidence intervals are wide and the power of the study is limited by the great dispersion of the data; the precision of the estimations would be improved by considering geographical incidence. Nevertheless, our projections are consistent with Wilesmith's survey of rendering plants relating the emergence of BSE to the dramatic fall in the proportion of meat and bone meal following solvent extraction, initiated in the late 1970s (65% in 1977 to 10% in 1983).

Quantitation of experimental postsurgical edema.

Many oral surgical procedures are followed by varying degrees of edema. Although numerous methods of minimizing swelling have been advocated, no technique has gained complete acceptance. A major problem has been the inability to document the efficacy of suggested treatments convincingly. The present study quantitates edema by measuring differences in percentage of water content between operated and unoperated tissues over a period of one week. Percentage difference in water content peaked by 48 to 72 hours and was followed by gradual resolution. By use of this model system, a steroid-induced, dose-dependent suppression of postsurgical swelling was confirmed.