Effects of climate on the cholera outbreak in Iran during seven years (2000-2006)

Recently, the role of the environment and climate in disease dynamics has become a subject of increasing interest to many scientists including microbiologists, clinicians, and epidemiologists. In this study, cholera outbreak during seven years (2000-2006) and climate factors were investigated. This study showed that there is a strong link between cholera outbreak and climate factors. When the temperature was <21.5°C the outbreak started and when the temperature raised at 42°C, the outbreak finished. However, the percentage of humidity had the same effect when it was 14% the outbreak begun and when it raised to 89% the outbreak finished too. In addition, the rate of rainfall also effected (i.e., when the minimum rainfall was 34.4 mm, the outbreak occurred and maximum rainfall raised to 567.9 mm the outbreak continued too.

Keywords: Cholera, climate, diseases, Iran

Cholera is a highly contagious disease, and is transmitted primarily by ingestion of faecally contaminated water by susceptible persons. Besides water, foods have also been recognized as an important vehicle for transmission of cholera. Foods are likely to be faecally contaminated during preparation, particularly by infected food handlers in an unhygienic environment. ^[1]

Cholera is still a main problem in many countries (i.e., in Peru, in 1991 after an absence of cholera incidence for 100 years) which spread rapidly in Central and South America, with recurrent epidemics in 1992 and 1993 ^[2] in Bangladesh (Rowland 1986), Mexico, ^[3] and former USSR. Little is known regarding the relation between cholera outbreaks and climate factors. However, a few research showed strong relationship of rainfall and infectious diseases outbreaks. ^{[4],[5],[6],[7],[8]} Also little is known about the link of climate factors such as temperature. ^[1],[6],[9] The purpose of this study was to discover the relation between such weather conditions and daily temperature and other climate factors in cholera outbreaks. Because cholera outbreak in Iran occurred occasionally, this study persuaded. In this study, the relation of climate factors to cholera outbreaks was investigated during 7 years (1998-2004), to determine hypothesis was arised that if there is any possibility link between climates factors and cholera outbreak. Also we intent to find out which climate factors are the most effective on outbreaks. Cholera caused by Vibrio cholerae , lends itself to analyses of the role of climate in infectious disease. The relationship between human health and climate is not a new concept, nor is it a new subject. In fact at least as far back as Hippocrates, many believed that human health was intricately linked to the seasons, local weather patterns, and other environmental factors. ^[10] During the past few years, scientists and several agencies, including the World Health Organization, American Academy of Microbiology, Intergovernmental Panel on Climate Change (IPCC), and United States. Global Change Research Program, among others, have published papers and issued reports highlighting the topic of climate and health. ^{[11],[12],[13],[14],[15],[16],[17],[18]} This disease has a historical context linking it to specific seasons and biogeographical zones.

Although cholera is an ancient disease and had disappeared from the most of developed world during the second half of the Twentieth Century, it persists in many parts of the world with serious epidemics, most often centered in tropical areas. The association between the disease and water has been long held in folk tradition, but was first established epidemiologically in the 1850s when John Snow made the link between the disease and a shallow well in London, United Kingdom. ^[19] Subsequently, extensive studies demonstrated that V. cholerae is, in fact, native to coastal ecosystems. ^[20] Vibrios, including V. cholerae , can be found in virtually any coastal water body, especially in the tropics and subtropics, when appropriate techniques are used. Recently, ecologically based models have been developed which define the role of environmentally, weather-, and climate-related variables in outbreaks of the disease. ^{[21],[22],[23]}

This study as a cross-sectional study was designed in Iran between 2000 and 2006 to find out the possible link of climate factors and cholera outbreaks. In this regard, the climate data were collected from Iran metrology organization based on daily collection of climate condition across the country. In addition, the cholera cases were registered and inserted in computer by co-operation of Iran Center of Diseases Control in Ministry of health during the same years of the study. Both data were inserted, analyzed, and compared with SPSS version 11.5.

The result of this study was shown in [Table 1],[Table 2] in aspect of number of cases of cholera and condition of weather during 2000-2006, respectively. The number of Cholera cases in different year (2000-2006) with place and time of outbreak was showed in [Table 3]. In addition, the climate data in different year (2000-2006) was showed in [Table 4] too.

Not only there are strong link between climate factors and bacterial diseases, but also different studies were confirmed link of vector borne diseases and climate. ^[14],[17] Climate variability and change in the United States: potential impacts on vector- and rodent-borne diseases water borne ^[24] and airborne diseases, ^[11] and climate too. In fact, vector-borne diseases are those that require a host (most often arthropods or rodents) to transmit a pathogen. Variability in climate and weather can affect both the vector population and the amplification of the pathogen within the host. Malaria and dengue fever continue to be the most-important vector-borne diseases worldwide. ^[18] The geographical range of the vector population is indicative of ecological and climatic conditions that limit the distribution of both the host and the pathogen. Often, ecological disturbances, including weather-related events, can cause a shift in host vectors or change in habitat that results in a greater likelihood of the pathogen coming in contact with humans, thus increasing the risk of human infection. ^[18] In border areas where conditions are not optimal for the pathogen and/or vector, small ecological disturbances or changes in weather may also alter conditions for disease transmission by creating a more favorable environment. ^[17] It is often in such border regions that the most-dramatic results of climate change and/or variability are recognized. In the recent literature, many researchers have documented relationships between changes in weather due to the ENSO and certain vector-borne disease outbreaks. ^{[25],[26],[27],[28]} In another example, the quality and quantity of drinking water, irrigation water, and environmental and/or recreational waters can be associated with changes in environmental conditions including weather- or climate-related variables. Floods may cause the overflow of wastewater treatment plants, failure of septic systems, or combined sewer overflows, which could contaminate nearby surface waters or wells. Furthermore, there is increasing concern about pathogens in storm water runoff. ^[24] Maintaining sanitary water conditions is also an issue during drought conditions, when contaminants may become concentrated in available water. Additionally, the likelihood of multiple uses in a water body may increase (e.g., for cleaning, bathing, and drinking) during droughts and consequently enhance the risk of contamination and exposure. Increasingly, the importance of the effect that weather and climate have on water quality, and not simply quantity, is being realized. Severe weather events appear to be correlated with enteric diseases, such as outbreaks of cryptosporidiosis related to excessive demand placed on sewage treatment plants from heavy rains and flooding. A retrospective study of drinking-water-related outbreaks of acute gastrointestinal illness in the United States by Rose et al. [29] revealed that 20% and 40% of groundwater and surface water outbreaks, respectively, between 1971 and 1994 were statistically associated with extreme precipitation. Other work has also demonstrated an ENSO connection to rates of enteric illness ^[30],[31] in South America, levels of enteric microorganisms in coastal areas of south Florida (United States), ^[32],[33] and cholera in Bangladesh. ^{[5],[23],[34]} Humidity, however, may affect survival of aerosolized virus particles. ^{[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[34],[35],[36],[37],[38],[39],[40]} In our study, we have found that the duration of outbreak is different year by year, for example, in total 345 cases of cholera (serogroup Ogawa) were seen in year 2000 and in 2001 105 cases of cholera (104 cases of serogroup Ogawa and 1 case of Inaba serogroup) were seen. Again in 2002, 118 cases of Ogawa were seen, in 2003 only 69 cases of Ogawa serogroup were seen too. In addition in 2004, 94 cases of Ogawa serogroup were reported and finally in 2005 1133 cases of cholera (1112 cases of Inaba serogroup and 21 cases of ogawa) were seen. In addition no cases of HiKojima serogroup were seen at the time of study.

DOI: 10.4103/1755-6783.50682

[Table 1], [Table 2], [Table 3], [Table 4]