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Cholera Cases: Past, Present, and Future
Abstract & Commentary
By Mary-Louise Scully, MD
Director, Travel and Tropical Medicine Center, Sansum Clinic, Santa Barbara, CA
Dr. Scully reports no financial relationship relevant to this field of study.
Synopsis: Although imported cholera cases in developed countries such as France may continue to decline, the global number of cholera cases continues to rise at an alarming rate. Orally administered cholera vaccine may hold promise in controlling cholera epidemics.
Source: Tarantola A, et al. Retrospective analysis of the cholera cases imported to France from 1973 to 2005. J Travel Med 2007; 14(4):209-214.
This retrospective analysis reviews details of the 129 proven cholera cases imported to France between January 1, 1973, and December 31, 2005. All strains were identified as Vibrio cholerae serogroup 01. The peak years of activity were 1980-1989, when most patients acquired their illness while visiting Morocco and Algeria, likely as a result of immigrants returning to these countries to visit friends and relatives. This trend disappeared, resulting in no further cases from Morocco or Algeria after the year 2000, as these countries essentially became cholera free. Since 1996 the geographic sources of imported cholera acquisition in France have been travel to Africa, mostly West Africa, or Asia.
The mean age of patients was 35 years, but during 1980-1999 there was a relatively higher proportion of imported cases in the younger ages (0-15) and older patients (over 66). The majority of patients (82%, n = 57) required hospitalization and a total of 2 deaths occurred. There was a significant seasonality with 82% of cases being reported between May and September. Cholera cases were reported from a wide variety of regions in France, and not just the larger cities with significant immigrant populations, such as Paris, Lyon, or Marseilles. In addition, the diagnosis of imported cholera was increasingly made in the nonteaching hospitals of France.
The historical trend of imported cholera cases in French travelers, initially after travel to Morocco and Algeria, but more recently after travel to other areas of Africa and Asia, is consistent with the pattern for global cases reported to the World Health Organization (WHO). The number of imported cholera cases is small relative to the impressive numbers reported from endemic areas. In 2006, the number of cholera cases reported to the WHO soared to 236,896, up from 131,943 cases in 2005 (overall increase of 79%).1 The majority of cases were from Africa (234,349 cases), followed by Asia (2,472), with India reporting most of the Asian cases (1,939 cases). A total of 33 countries in Africa reported cholera cases, but the African countries with the greatest burden of disease were Angola, Ethiopia, Sudan, and Democratic Republic of the Congo. Together, these 4 countries alone reported 186,928 cases with 4,988 deaths. The United Republic of Tanzania had an almost 5-fold increase in cases compared to 2005 with 14,297 cases. Malawi, Mozambique, Zambia, and Zimbabwe all reported increased numbers of cholera cases in 2006.
Despite these impressive numbers, the WHO estimates that cholera cases remain underreported. One reason is that not all countries consistently report cholera cases to the WHO. For example, several cholera outbreaks in 2004 on the Indian continent and Southeast Asia (Bangladesh, Myanmar, and Pakistan) occurred, yet they were not reported to the WHO.2 Another reason for underestimation of cholera is that milder cases may not seek medical care, and a stool specimen may not be obtained. Lastly, the fear that negative publicity regarding a cholera outbreak will adversely affect the tourism industry in a developing country may also contribute to underreporting.
Orally administered cholera vaccine (OCV) offers some promise in controlling cholera epidemics. A mass immunization program using an oral, inactivated, whole cell, recombinant vaccine cholera toxin B subunit (WC-rBS)) for 19,550 non-pregnant individuals in Beira, Mozambique was associated with 78% protection.3 The WHO has now prequalified this vaccine (Dukoral™ ) for use in the setting of cholera outbreaks. Two doses (3 doses for children ages 2-6) are given at least one week apart. Booster doses are given after 2 years for children older than 6 years and adults but children 2-6 years are given a booster after 6 months. This vaccine is also licensed for short-term protection (< 3 months) against diarrhea caused by ETEC (enterotoxigenic Escherichia coli). The vaccine is available in the UK, Canada, and many other countries such as Peru, Thailand, and Sweden, but is not yet available in the United States.
Countries without access to safe water and basics of adequate sanitation will remain at risk for epidemic cholera disease. The latest country to be added to the list is Iraq with 3,182 cases of watery diarrhea, suspected as cholera, 9 deaths, and 283 stool isolates of Vibrio cholera reported by health official from just 5 out of 11 districts of Sulaymaniyah Governate as of September 6, 2007.4,5 The outbreaks are occurring in the Kurdish province of Sulaimaniyah and Kirkuk. Health officials in Iraq suspect the source of the outbreak is cracked water pipes that had allowed contamination by sewage. Unfortunately, the political instability of this war-torn country, the disruption of the existing infrastructure, the dwindling number of health care providers, and the lack of safe drinking water, are perfect ingredients for epidemic cholera disease.