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Biomedical subjects

P Y Boëlle

Publications and source records attributed to P Y Boëlle.

18 recordsLinked to original sources
PubMed2005

Penicillin-resistant pneumococcal meningitis: high antibiotic exposure impedes new vaccine protection.

The frequency of meningitis due to penicillin-resistant Streptococcus pneumoniae (PRP) has increased in recent years, making treatment failure more likely. It is currently expected that pneumococcal conjugate vaccines might curb this trend. We investigated this issue using a mathematical model applied to the current prevalence of resistance and antibiotic exposure in the United States and in France. Our main finding was that the level of antibiotic exposure may limit the effect of the vaccine. In relatively low antibiotic exposure environments such as the United States, large-scale vaccination prevents a large part of PRP meningitis cases, whereas in high antibiotic-exposure environments such as France, vaccination alone does not lead to a substantial reduction in PRP meningitis incidence. Our results suggest that antibiotic exposure reduction will remain of primary importance for the control of PRP meningitis despite wide scale use of pneumococcal conjugate vaccines.

Adolescent↗
PubMed2004

A Bayesian MCMC approach to study transmission of influenza: application to household longitudinal data.

We propose a transmission model to estimate the main characteristics of influenza transmission in households. The model details the risks of infection in the household and in the community at the individual scale. Heterogeneity among subjects is investigated considering both individual susceptibility and infectiousness. The model was applied to a data set consisting of the follow-up of influenza symptoms in 334 households during 15 days after an index case visited a general practitioner with virologically confirmed influenza. Estimating the parameters of the transmission model was challenging because a large part of the infectious process was not observed: only the dates when new cases were detected were observed. For each case, the data were augmented with the unobserved dates of the start and the end of the infectious period. The transmission model was included in a 3-levels hierarchical structure: (i) the observation level ensured that the augmented data were consistent with the observed data, (ii) the transmission level described the underlying epidemic process, (iii) the prior level specified the distribution of the parameters. From a Bayesian perspective, the joint posterior distribution of model parameters and augmented data was explored by Markov chain Monte Carlo (MCMC) sampling. The mean duration of influenza infectious period was estimated at 3.8 days (95 per cent credible interval, 95 per cent CI [3.1,4.6]) with a standard deviation of 2.0 days (95 per cent CI [1.1,2.8]). The instantaneous risk of influenza transmission between an infective and a susceptible within a household was found to decrease with the size of the household, and established at 0.32 person day(-1) (95 per cent CI [0.26,0.39]); the instantaneous risk of infection from the community was 0.0056 day(-1) (95 per cent CI [0.0029,0.0087]). Focusing on the differences in transmission between children (less than 15 years old) and adults, we estimated that the former were more likely to transmit than adults (posterior probability larger than 99 per cent), but that the mean duration of the infectious period was similar in children (3.6 days, 95 per cent CI [2.3,5.2]) and adults (3.9 days, 95 per cent CI [3.2,4.9]). The posterior probability that children had a larger community risk was 76 per cent and the posterior probability that they were more susceptible than adults was 79 per cent.

Adolescent↗
PubMed2004

Short- and long-term effects of pneumococcal conjugate vaccination of children on penicillin resistance.

Recent observations have shown that wide-scale vaccination with pneumococcal conjugate vaccines was associated with a reduction in invasive disease, supporting the expectation that vaccination could help reduce carriage of Streptococcus pneumoniae and control the spread of resistant strains. However, it is too early to assess whether these effects can be sustained in the long term. Here, we used mathematical modeling to investigate time changes in pneumococcal colonization and resistance induced by conjugate vaccination in an environment where antibiotic exposure is high and resistance is widespread. According to model predictions, vaccination induced a decrease in carriage of vaccine-type pneumococci to very low levels, typically in 10 to 15 years under epidemiologically realistic conditions. Almost simultaneously, non-vaccine-type pneumococci spread in the community. Consequently, while there was a short-term decrease in the overall carriage rate, it was followed after a few years by a renewed, although limited, increase. Vaccination with a heptavalent vaccine did not affect the extent to which antibiotic resistance was selected: in all cases, the distribution of resistance levels peaked at high levels (MIC > 2 microg/ml) after 20 years. With a vaccine optimally designed to include all serotypes currently exhibiting decreased susceptibility to penicillin G, the selection of resistance was slowed down, although not prevented. These results suggest that because of serotype replacement, the effects of vaccination observed today may not be sustained in the long term. As a consequence, vaccination alone may not be successful in controlling selection for resistance in S. pneumoniae.

Algorithms↗
PubMed2003

Blue light dose distribution and retinitis pigmentosa visual field defects: an hypothesis.

The hypothesis that retinitis pigmentosa (RP) is worsened by blue light has been raised a century ago. In order to check this hypothesis we calculated the theoretical dose distribution of light on the retinal surface. The relative dose to the different parts of the retina was calculated using a Monte-Carlo method. The changes in the peripheral isopters were calculated both degrading at a constant rate and degrading proportionally to light exposure. There is a considerably greater exposure to the superior compared to the inferior visual field. The maximum dose of UV and blue light is located on the superior field about 4mm above the macula. The dose received by the peripheral retina is markedly lower than the dose received by the central retina. The visual field defects most commonly described in RP are concentric, centered by the macula. These defects cannot, therefore, be explained by the impact of light on the retina. But some regional form of RP with a superior field defect can result from an abnormal genetically encoded sensitivity to ultraviolet and blue light.

Dose-Response Relationship, Drug↗
PubMed2003

[Postnatal growth delay in 27 to 33 week premature infants: frequency and risk factors. Retrospective study of 161 cases].

UNLABELLED: The optimization of the nutrition of very low birth weight premature neonates has become a major concern given the improvement in survival for these children. The goal of the recommended nutritional intakes is to reach a quantitative and qualitative growth similar to the in utero growth. The objectives of this study were to analyze the anthropometric data at birth and near term in a cohort of premature neonates with birth weight appropriate for gestational age and to try to determine risk factors of postnatal hypotrophy. POPULATION AND METHODS: We conducted a retrospective study over three years (1998-2001) in the neonatology unit of the Armand Trousseau Children's Hospital, Paris, France. The inclusion criteria was a gestational age under 33 weeks with birth weight appropriate for gestational age. Data were collected at admission, during hospitalisation and at discharge and a standardised form was filled for each child. We defined postnatal hypotrophy (PNH) as an hypotrophy at discharge (weight < 10(th) centile according to the Audipog reference curve) in neonates with birth weight appropriate for gestational age. RESULTS: One hundred and sixty one neonates were included. Eighty two had PNH. In univariate analysis, factors significantly associated with PNH were: birth weight, gestational age, length of hospitalisation, the occurrence of nosocomial infection, of enteropathy, preeclampsia, neonatal asphyxia and antenatal corticoid treatment. In multivariate analysis, risk factors of PNH were: low birth weight, low gestational age and the occurrence of nosocomial infection. CONCLUSION: Our study shows that half of the appropriate for gestational age premature neonates were hypotrophic near term. The causes may be various: nutrition is not optimal and intercurrent factors may play a major role such as nosocomial infection.

Analysis of Variance↗
PubMed2003

Bacterial resistance to penicillin G by decreased affinity of penicillin-binding proteins: a mathematical model.

Streptococcus pneumoniae and Neisseria meningitidis have very similar mechanisms of resistance to penicillin G. Although penicillin resistance is now common in S. pneumoniae, it is still rare in N. meningitidis. Using a mathematical model, we studied determinants of this difference and attempted to anticipate trends in meningococcal resistance to penicillin G. The model predicted that pneumococcal resistance in a population similar to that of France might emerge after 20 years of widespread use of beta-lactam antibiotics; this period may vary from 10 to 30 years. The distribution of resistance levels became bimodal with time, a pattern that has been observed worldwide. The model suggests that simple differences in the natural history of colonization, interhuman contact, and exposure to beta-lactam antibiotics explain major differences in the epidemiology of resistance of S. pneumoniae and N. meningitidis.

Bacterial Proteins↗
PubMed2002

Varicella in non-immune persons: incidence, hospitalization and mortality rates.

This study was conducted to estimate the varicella morbidity and mortality rates per age group among the non-immune population in France. Morbidity and mortality data for the years 1990-9 were derived from nationwide databases and surveillance systems. An incidence/prevalence model was designed to quantify the non-immune population per age group. The incidence of varicella in the non-immune population peaks during childhood and again in the 25-35 years age group. For children aged 1-4 years, adults aged 25-34 years and those older than 65 years, the hospitalization rates are respectively 235, 1,438 and 8,154 per 100,000 cases, and the death rates are respectively 7, 104 and 5,345 per million cases. Case fatality or case hospitalization rates were not evenly distributed among adults and increased dramatically with age.

Adolescent↗
PubMed2001

Comparison of the statistical efficiency of case-crossover and case-control designs: application to severe cutaneous adverse reactions.

Although case-crossover analyses have lately emerged as an alternative to case-control analyses in epidemiological studies, it is not yet known in which situations they give reliable conclusions. In this work, the case-crossover and the case-control designs were first compared on the basis of a dataset from a published study of severe cutaneous adverse reactions resulting from drug exposures of various durations and prevalences of use (245 cases, 1147 controls, and exposures to 23 drug classes). Next, the statistical efficiency of each design was compared via Monte Carlo simulations. Eight of the 13 risk factors identified by case-control analysis of the published data were also identified by the case-crossover analysis, with fairly good agreement on ranks of risk estimates (Spearman's correlation coefficient = 0.71, P < 0.001 ). Simulation studies showed that for relative risks below 8, the case-crossover design (250 cases, 4 control periods/case) had a higher power than the case-control design (250 cases, 4 controls/case), and that the case-crossover design was more conservative than the case-control design for prevalences of drug use below 10%. We conclude that the case-crossover design is not suitable for long-term exposures, but is an appropriate alternative for assessing rare risks associated with transient to short-term exposures.

Case-Control Studies↗
PubMed2000

Risk factors of acute diarrhoea in summer--a nation-wide French case-control study.

The aim of this study was to identify risk factors for acute diarrhoea (AD) during the summer in France. A matched case-control study was conducted at a national level among patients of 500 general practitioners (GPs). From July to September 1996, 468 case-control pairs were included. Cases were more likely than controls (i) to live away from their main residence (OR 3.0; 95% CI 1.6-5.7), (ii) to have returned from a country at high risk of AD (OR 4.6; CI 0.9-23.1), and (iii) to have been in contact with a case of AD (OR 2.0; CI 1.3-3.1). A significantly decreased risk of AD was found for consumption of well-cooked chicken (OR 0.5; CI 0.3-0.8) and raw or undercooked home-made egg-containing products (OR 0.6; CI 0.4-0.8). These findings suggest that travel to high-risk areas, or travel within France, and being in contact with a case of AD, are risk factors for the occurrence of AD in summer in France.

Adolescent↗
PubMed2000

Voluntary reporting system in anaesthesia: is there a link between undesirable and critical events?

BACKGROUND: Reporting systems in anaesthesia have generally focused on critical events (including death) to trigger investigations of latent and active errors. The decrease in the rate of these critical events calls for a broader definition of significant anaesthetic events, such as hypotension and bradycardia, to monitor anaesthetic care. The association between merely undesirable events and critical events has not been established and needs to be investigated by voluntary reporting systems. OBJECTIVES: To establish whether undesirable anaesthetic events are correlated with critical events in anaesthetic voluntary reporting systems. METHODS: As part of a quality improvement project, a systematic reporting system was implemented for monitoring 32 events during elective surgery in our hospital in 1996. The events were classified according to severity (critical/undesirable) and nature (process/outcome) and control charts and logistic regression were used to analyse the data. RESULTS: During a period of 30 months 22% of the 6439 procedures were associated with anaesthetic events, 15% of which were critical and 31% process related. A strong association was found between critical outcome events and critical process events (OR 11.5 (95% confidence interval (CI) 4.4 to 27.8)), undesirable outcome events (OR 4.8 (95% CI 2.0 to 11.8)), and undesirable process events (OR 4.8 (95% CI 1.3 to 13.4)). For other classes of events, risk factors were related to the course of anaesthesia (duration, occurrence of other events) and included factors determined during the pre-anaesthetic visit (risk of haemorrhage, difficult intubation or allergic reaction). CONCLUSION: Undesirable events are associated with more severe events and with pre-anaesthetic risk factors. The way in which information on significant events can be used is discussed, including better use of preoperative information, reduction in the collection of redundant information, and more structured reporting.

Anesthesia↗
PubMed2000

Automatic coding of reasons for hospital referral from general medicine free-text reports.

Although the coding of medical data is expected to benefit both patients and the health care system, its implementation as a manual process often represents a poorly attractive workload for the physician. For epidemiological purpose, we developed a simple automatic coding system based on string matching, which was designed to process free-text sentences stating reasons for hospital referral, as collected from general practitioners (GPs). This system relied on a look-up table, built up from 2590 reports giving a single reason for referral, which were coded manually according to the International Classification of Primary Care (ICPC). We tested the system by entering 797 new reasons for referral. The match rate was estimated at 77%, and the accuracy rate, at 80% at code level and 92% at chapter level. This simple system is now routinely used by a national epidemiological network of sentinel physicians.

Confidence Intervals↗
PubMed1999

Risk of hepatitis C virus transmission to surgeons and nurses from infected patients: model-based estimates in France.

BACKGROUND/AIM: The aim of this study was to estimate the annual number of cases of hepatitis C virus transmission from infected patients to uninfected surgeons or nurses due to percutaneous injury during invasive procedures. METHODS: The risk of transmission was estimated using a model involving three probabilities: A, that a health care worker sustains at least one percutaneous injury during a procedure; B, that 1 to 10% of patients are seropositive for hepatitis C virus; and C, that infection by this virus is transmitted to the Health Care Worker after such exposure. Probability A was estimated from the results of 2 French multicentric prospective trials. Probability C was estimated from the results of 9 international prospective studies. A ten-fold decreased risk was assumed for surgeons who wear gloves and use solid-bore suture needles. RESULTS: During a single procedure, the estimated probability of hepatitis C virus transmission from an infected patient to an uninfected surgeon ranged from 4.2x10(-5)% to 4.2x10(-4)%, and from 2.98x10(-6)% to 2.98x10(-5)% to an uninfected nurse. For surgeons, the estimated annual cumulative risk of occupational infection ranged from 0.01% to 0.1% (1 in 10000 to 1 in 1000), and for nurses from 0.0054% to 0.054% (1 in 18700 to 1 in 1900). CONCLUSIONS: Between 2 and 21 surgeons out of a total 20000 are estimated to acquire occupationally-related hepatitis C virus infection, and between 16 and 167 nurses out of a total 300000. These estimates strongly justify introducing preventive measures to protect health care workers from bloodborne infection.

France↗
PubMed1998

Global and partial agreement among several observers.

The advantage of modelling agreement on a categorical scale among observers rather than using summarizing indices is now well established. However, analysis of agreement among more than two observers is essentially based on pairs of observers. We present a global and partial agreement modelling approach derived from the quasi-independence and quasi-symmetry log-linear models. This approach addresses high order interactions in the contingency table rather than two-way interaction in the pairwise agreement approach. Pairwise, global and partial agreement models were applied to the detection by six pathologists of three lesions in biopsy specimens arising from patients suspected to be affected by Crohn's disease. The global and partial agreement approach surpasses the pairwise agreement approach, especially if there is heterogeneity among ratings.

Biopsy↗
PubMed1998

SHARE: a tool to analyze and assess strategies in health care organization management.

In health care organizations, management of both human and material resources implies decision making. When seemingly equivalent strategies are possible, simulation can help to make a decision on better grounds. The SHARE workframe was designed to address the specificities of health care and to provide a comprehensive environment for modelling and simulating health care processes. The typology of objects is defined as Actors, subdivided in Clients and Resources and Elementary Operations. Graphical tools allow us to build processes from these objects and to create their relationships. Various strategies based on either clinical or managerial changes may be investigated. After a simulation, graphical tools allow us to display summary information on the utilization of all actors, waiting times, and goodness of execution. The use of SHARE is exemplified with the analysis and simulation of changes in the Pulmonary Function Testing Laboratory of the Saint-Antoine Hospital, Paris.

Computer Simulation↗
PubMed1998

Modelling health care processes with SHARE.

This paper describes the "SHARE" workframe, designed to provide a comprehensive environment for modeling and simulating health care processes. The objects defined within SHARE are Actors, subdivided in Clients and Resources, and Elementary Operations. Graphical tools allow to build processes from these objects, and to specify their relationships. Various strategies based on either clinical or managerial changes may be investigated. Summary information on the utilization of all actors, on waiting times and goodness of execution may be displayed after a simulation. Better description of processes, and their study a priori will improve reliability, quality of care and satisfaction of patients.

Appointments and Schedules↗
PubMed1996

A sequential procedure to test the progressive decrease of rare adverse events.

A program to construct the Rapid Sequential Test (R-ST), a sequential procedure to test the decrease of the rate of rare adverse events, is described. This sequential procedure is constructed with the Sequential Probability Ratio method. It relies on a model for the progressive decrease in the rate of adverse events from a given initial rate to a target rate, during a transition period. The program allows one to calculate the bounds of rejection of the R-ST, and to study its power under various types of decrease. It is shown that the R-ST gives a conclusion faster than standard sequential procedures for the same type I and II error, saving at least one quarter of the trials completed during the transition period. The use of the software to construct R-STs is discussed with respect to the specification of the model.

Blood Transfusion↗
PubMed1996

[Quality assurance and prevention of immuno-hemolytic incidents in blood transfusion].

Direct and indirect measures of the reliability of the transfusion process are described. These measures can be used to assess the improvement of the transfusion process with a view to preventing hemolytic incidents. Quality assurance arrangements required by their use are made clear. The stress is put upon four points: processes must be formalized and standardised; quality audits must become a routine part of the transfusion process; the system of error reporting must be extended to include all failures; anonymity must be insured to improve reporting.

Anemia, Hemolytic↗