CROHN'S DISEASE VIEWPOINT

Hygiene, environmental and socioeconomic determinants of Crohn's disease -
towards an aetiological hypothesis

Higijena, cinioci  spoljne sredine i socioekonomske determinante Crohn-ove bolesti - put  ka etiološkoj hipotezi

Mihailo Alic

During my visit to Belgrade, Professor Perisic had asked me to contribute a short viewpoint article and
summarise my year long research of Crohn's disease epidemiology. Rather than simply compile my
previous articles, I decided to incorporate observations of Crohn's disease experts I've met there
and further support my aetiological hypothesis published in the American Journal of Gastroenterology
(1, 2).

I have entered Crohn's disease epidemiology with a Letter to the Editor commenting on a study that
supported a hypothesis of better sanitation in early childhood as a risk factor for later development
of this disease ( 3 ). The hypothesis further relied on observation that in developing countries, where
infant mortality is higher, Crohn's disease is much less frequent than in the developed world. Early
childhood events may modulate immunological response to enteric pathogens later in life,
predisposing to Crohn's disease individuals who were protected from this exposure in childhood by
better sanitation. Among studies that contradict the model of a sheltered child as a potential Crohn's
patient I have found most convincing a high incidence of the disease in South Asian immigrants in
England, while the incidence is very low in their home country. Currently I do not stand firm on
opposing the above mentioned hypothesis since one could argue that those who were able to
emigrate may not be from social classes with high infant mortality, so the matter warrants further
study. On the other hand, individuals who in the early childhood had running hot water in their homes
belong to higher socioeconomic backgrounds, and one can argue that this has predisposed them to
Crohn's disease.

That socioeconomic factors have significant influence in Crohn's disease is obvious both on micro
and on macro level. Countries that are more developed have higher incidence, and the same has
been shown for individuals within a country. I have shown that workforce participation of sex and
race groups also correlates to Crohn's incidence, further supporting the influence of the economic
factor ( 4 ). I have also spent considerable time collecting data on gender incidence differences ( female to  male, F/M incidence ratio ) and their temporal and geographic distribution. Crohn's F/M incidence
ratio was higher in countries where women had higher workforce participation and has increased in
time following trends in workforce composition.

Exposure to a Crohn's patient may be another major risk factor and, as will be hypothesized further,
may also explain higher socioeconomic status observed. Infectious etiology of this disease has been
suspected from the early days of its epidemic, but final proof still eludes us. Animal experiments from
the 1970's have fulfilled certain Koch's transmission postulates, but infection agent is still unknown.
Nevertheless, there is an abundance of indirect proof to testify to its communicability - higher than
expected by chance incidence in spouses of patients, geographic, communal and familial clusters,
increased frequency of abnormal intestinal permeability in spouses and relatives proportional to the
length of association and frequency of contacts with a patient ( 5 ). If a close and prolonged contact
with a Crohn's patient is a risk factor for this mainly intestinal disease, it may be fruitful to examine a
possible fecal-oral route of transmission. I have investigated eating out as a way of contracting this
unknown infectious agent and a behavior that is closely related to a higher socioeconomic status.
Economic statistics for the U.S. have shown normalized expenses on food away from home to have
followed other economic parameters and Crohn's disease incidence with stagnant 1950's and rise in
the 1960's that was stopped temporary at the end of the 1970's. Since Crohn's disease is still not
considered contagious, patients are not precluded from working in the food industry, and there is
always a possibility of subclinical or undiagnosed disease.

Yugoslavia is an interesting country for studying Crohn's disease epidemiology and its socioeconomic
determinants because of its modest socialist past, and war-torn present. Unlike developed countries
of the Western Europe and the U.S. where preponderance of urban population of higher
socioeconomic status is observed in Crohn's disease incidence, here observations favor rural
inhabitants and minority ethnic groups like Gipsies and Albanians. Urban population has experienced
the most impact of war-torn economy and political sanctions, and eating out is even less prevalent
than a decade ago when it was still inferior to western standards of living. Eating out and restaurants
are almost non-existent in a situation where majority of people are barely making ends meet. On the
other hand, world reports from the 1960's have observed Crohn's disease favoring Jews, which
other than possible genetic influence and their overall higher economic status may be explained by
their closer social ties. This latter can be also claimed for Gipsies and Albanians, and possible
communal transmission may be hypothesized. It is obvious that this disease is not easily transmissible,
yet its incidence has risen in all countries where it has been reported. Epidemiological study starting
in January of 2000 in Yugoslavia is a part of Mediterranean Medical Society IBD Group study, and
we are all looking forward to data collected to further contribute to our understanding of Crohn's
disease.

Address correspondence to:
Mihailo Alic, Independent Researcher
3720 Balboa St.
San Francisco, CA 94121, USA
e-mail: [email protected]
 

References:

1. Alic M. Socioeconomics of Crohn's disease - clues for an etiological hypothesis. Am J
Gastroenterol. 2000;95:324-6.

2. Alic M. Crohn's disease epidemiology at the turn of the century - solving the puzzle. Am J
Gastroenterol. 2000;95:321-3.

3. Alic M. Is poor sanitation a risk factor for developing Crohn's disease? Am J Gastroenterol.
1999;94:1113.

4. Alic M. Workforce composition and the sex ratio of Crohn's disease incidence. Am J
Gastroenterol. 1999;94:3652.

5. Alic M. Is the exposure to a Crohn's patient an environmental factor for developing the disease?
Gut 1999;45:631.