Tag Archives: epidemiology

Multiple sclerosis, what about the south-north gradient?

4 Jan

Recent researches found that the south north gradient of the occurrence of multiple sclerosis is diminishing in the USA and doesn’t exist anymore in France.
Here are the two articles:

Alvaro Alonso, MD Miguel A. Herna ́n, MD
Temporal trends in the incidence of multiple sclerosis A systematic review
Neurology 71 July 8, 2008
Available in full text here:

Click to access 129.pdf

Fromont A, Binquet C, Sauleau EA, Fournel I, Bellisario A, Adnet J, et al. Geographic variations of multiple sclerosis in France. Brain 2010;133:1889-99.OpenUrlAbstract/FREE Full Text http://brain.oxfordjournals.org/content/brain/133/7/1889.full.pdf

Thus the epidemiology of multiple sclerosis seems to shift toward a less intense south north gradient but in the same time an aggravation of the sex ratio, aggravating the burden that women bear in this inflammatory disease that affects the central nervous system (i.e. the central unit of our body in terms of information technologies).

This tendency opens new interests for more epidemiological studies in this field. All the more because the observational studies aiming to prove the mixed, genetic and environmental, etiology are entangled with the current migrations of populations, the mobility of young people in view of finding a job and the changes in life habits in the populations of the south such as using more protection against the sun rays.

Professor Confavreux had well depicted the stakes in this editorial:

An unchanging man faced with changing times Christian Confavreux
DOI: http://dx.doi.org/10.1093/brain/aws135 1663-1665 First published online: 24 May 2012

For the present moment multiple sclerosis etiological mechanism is an enigma and risks to remain so if researchers in the domain have no new data to crunch at the populational level.



18 Oct

Epidemiology and geography since long ago share common interests.
Epidemiologists have always searched the causes of contagious diseases by locating the very place where the outbreak began. Hence the necessity to develop sophisticated geographical statistical analysis methods in order to localize the point from where the disease originates and then spread across the country. But nowadays those methods are also implemented by searchers to highlight high concentrations of non epidemic, chronic, degenerative diseases in a given country. Here the causal agent is no more a bacteria nor a virus but indeed a spot of concentration of social inequality (or pollution, depending of the research question ). If a geographical concentration exist of lack of knowledge of what a healthy behavior is, or of low incomes restraining access to a healthy life, then the analysis should uncover a higher prevalence of the degenerative disease at less this is the hypothesis. Here below is a link toward a paper very accurate in demonstrating how different geographical statistical analysis methods can lead to a variation in the epidemiological results obtained. This point is crucial to consider because were it Ebola virus or social inequality or educational level context, causes of diseases will always have something to do with geography!

Historical cohorts: strengths and weaknesses

8 Jul

Historic cohort study, generally means to take a look back at events that already have taken place.


database (Photo credit: Sean MacEntee)

With the huge data bases containing Millions of lines of historic of several years of reimbursements of health care and health conditions now at the disposal of nation wide health care insurances like CNAMTS or RSI in France or Kaiser Permanente or Veteran Affairs in the USA , historical cohorts such as the one that is described in the article referenced below are very easy to implement provided that researchers have access to the data base and use the appropriate software to extract accurately the information to transform rough data in a relevant medical information. Personally I am a fan of SAS enterprise guide (no funding by SAS to disclose for this Blog).
But nothing being perfect in this world the weakness of such historical cohorts retrospectively rebuilt is that they can only put in evidence associations without absolutely no hint but the possible causation process involved in the association. Their force is of course the number of subjects analyzed (usually huge) and the provenance of the subjects (community and real life subjects as opposed as the carefully selected subjects of the controlled randomized trials).
But at the end of the day, to conclude like the study referenced below does, that high doses of ACE treatment causes a lowering of the mortality rate and the readmission rate is obviously going beyond the proper results of the study. Indeed no observational historic cohort, whatever the size of the analysed sample is, has the power to demonstrate a causality link. One possible explanation of the association unveiled by the study is that prescribers could be more reluctant to give high doses of ACE to the more fragile groups and comorbidity incurring groups of the studied population.

More content and referenced study:


Improved Outcomes in Heart Failure Treated With High-Dose ACE Inhibitors and ARBs: A Population-Based Study: full text research letter

Bad science (part two)

26 Nov
Cover of "Bad Science"

Cover of Bad Science

Look at this incredible video. The man who is talking is a medical practitioner who has become an epidemiologist. He belongs to a Cochrane group. The Cochrane groups chase false evidence-based medicine by reviewing all the published studies on a particular public health issue (like preventive behaviors, cancer screening, pharmaceutical industry lobbying and so on). It’s an awesome one man show made by a Doctor!

Vodpod videos no longer available.


3 Sep

Wandering in the Hervé Maisonneuve Blog I just have learned that Daniel Schwartz passed on sept 6, 2009 at the age of 92.
If you were en ancient student of the « Certificat d’Etudes Statistiques Appliquées à la Médecine (CESAM) » like I was this name invariably must remember you the green book which you learned “by heart” and which made you shake with terror before exam. We, students, all named this green book “The Schwartz”. In those years (1992) I choose the Epidemiological option of the CESAM and succeeded the exam. What happened next is just history…

Legionella and Dengue are tracked by Facebook and google

20 Jun

In a precedent post I talked about Google correlate (see my post of 9 June).

Social networks and search engines are becoming the two new disease hunters of the 21 century.

Legionellosis epidemic has been elucidated in Los Angeles County by the mean of Facebook and dengue is being actually chased by Google.

In the next future you will perhaps start your next trip abroad by connecting you to Google Dengue Trends to get an instant indicator of Dengue activity in the World or to Health Map.

An interesting research article on neglected tropical disease surveillance has been published on the subject in Plos (Public Library of Science).

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