Cross-posted from the American Geophysical Union’s GeoSpace blog.

Even though the deadly cholera epidemic in Haiti is now spreading more slowly, health officials are still working to prevent as many new cases as possible. Detailed models of the disease’s spread help those in charge of making public health decisions understand the effectiveness of control measures, from vaccines to investments in clean water supply and education.

A new study by Enrico Bertuzzo and colleagues just accepted for publication in Geophysical Research Letters looks at how the Haitian cholera outbreak is likely to evolve and finds that, now that the disease is a nationwide epidemic, clean water and hygiene education measures are likely to be more effective at reducing cholera’s residual progression in the country than a vaccination campaign.

Cholera bacteria (Vibrio cholerae) spread mainly through fecal contamination of water, and the study describes the two main mechanisms of that spread: hydrologic pathways (because the bacteria can survive and travel through aquatic environments) and travel by infected people (who may or may not exhibit symptoms). The researchers used a dispersion model and information about more than 500 Haitian communities to predict the spread of V. cholerae and the cholera cases that would result.

Based on their modeling (which the researchers carried out before mid January), the team predicted that new cases would start decreasing in January, and that is in fact what happened. In late January, Haiti’s health ministry reported that new cases had dropped to about 4,700 per week (a substantial decline since November, when 12,000+ new cases were reported each week). By then, cholera had killed nearly 4,000 people and sickened more than 194,000.

Bertuzzo’s team modeled the effect of a campaign to vaccinate 150,000 people (the maximum possible given the vaccine supply) in Port-au-Prince starting on January 1, 2011 and discovered the benefits would have been negligible. They note that this intervention’s small effectiveness is due partly to the slow pace at which full immunity builds up and to the likelihood that many vaccine recipients would’ve already built up natural immunity through asymptomatic infections.

By contrast, results suggest that clean water and hygiene education measures could be much more effective at reducing cholera’s residual progression in Haiti. The modeling assumed that these prevention measures would reduce the probability of ingesting contaminated water or food during a one-month timespan by 40%, and the authors note that the feasibility of achieving this under Haiti’s current conditions is debatable. Still, it’s useful for health officials to know what kind of target an intervention will need to achieve in order to reduce cholera’s progress. Then, they can focus on finding and deploying the resources necessary to make the intervention effective.

E. Bertuzzo, L. Mari, L. Righetto, M. Gatto, R. Casagrandi, M. Blokesch, I. Rodriguez-Iturbe, & A. Rinaldo (2011). Prediction of the spatial evolution and effects of control measures for the unfolding Haiti cholera outbreak Geophysical Research Letters : 10.1029

Comments

  1. #1 Onkel Bob
    February 18, 2011

    Isn’t the interval for the cholera vaccine 6 months? As I recall from my time in the military, the cholera vaccine was given to me at that frequency.
    Mind you 30 plus years ago and things may have improved.

  2. #2 Liz Borkowski
    February 18, 2011

    The administration instructions for Dukoral, the cholera vaccine that’s pre-qualified by the WHO, say:

    Primary immunization for adults and children 6 years and older:
    • 2 doses orally at least 1 week apart.
    • 1st dose at least 2 weeks before departure.
    • 2nd dose 1 week after the 1st dose at least 1 week before departure.
    • Protection against cholera starts 1 week after the second dose and will last for 2 years.
    • If more than 6 weeks elapse between the 1st and 2nd dose, the primary immunization
    should be re-started.

    Dukoral doesn’t even appear to be available in the US, although it was approved in Canada 2003 … so I’m guessing any cholera vaccine administered to troops before then was a different one.

  3. #3 sheelas
    February 18, 2011

    Even though we do immediate fix for existing problem, The best solution is to find the root cause of Haiti’s Cholera epidemic that are clean water and hygiene education measures. It is hard to implement but it can be possible.

  4. #4 plumbing
    February 19, 2011

    Yes. This can really help reduce the spread of cholera bacteria. All we need is time and attention in what is happening to our surroundings.

  5. #5 Davis
    February 19, 2011

    The best solution is to find the root cause of Haiti’s Cholera epidemic that are clean water and hygiene education measures.

    While Haiti’s infrastructure has allowed the cholera to spread more easily, the root cause of the problem was the Nepalese UN contingent, whose human waste was discharged in the vicinity of local water supplies. All testing indicates that the particular strain that has run rampant in Haiti was the same as the one running through Nepal not long ago.

    So maybe the secondary lesson is, keep a close eye on your local UN regiment.

  6. #6 Derek
    February 20, 2011

    Public awareness can lead to funding for vaccines. Health officials should immediately take effective short and long term measures to reduce cholera’s progress especially by putting more weight in educating the people of Haiti.

  7. #7 Chester Scott
    March 6, 2011

    It was probably, sadly, brought their by Nepalese UN troops. There had never been cholera in Haiti, and those guys came from a spot which JUST had an outbreak, and they WERE dumping raw sewage in the waterway despite numerous requests to stop.
    http://breastenlargementwarning.com/

  8. #8 Emily
    March 19, 2011

    It’s so sad to see Haiti in the state that they are in. It’s so awful to think that there are countries that don’t even have access to clean water. Hopefully more and more people will come to their aid.

  9. #9 formula 21
    March 21, 2011

    Public awareness can lead to funding for vaccines. Health officials should immediately take effective short and long term measures to reduce cholera’s progress especially by putting more weight in educating the people of Haiti.