A Cholera Outbreak Investigation in Province, : Matched Case-Control Study

Ghobad Moradi1, Mohammad Aziz Rasouli2, Parvin Mohammadi3, Elham Elahi4, Hojatollah

Barati5

1 Assistant Professor of Epidemiology, Social Determinants of Health Research Center,

Kurdistan University of Medical Sciences, Sanandaj, Iran

2 MSc Epidemiology, Department of Epidemiology & Biostatistics , Kurdistan University of

Medical Sciences, Sanandaj, Iran

3 Department of Nursing and Midwifery, Sanandaj Branch, Islamic Azad University, Sanandaj,

Iran

4 PhD candidate in health education and health promotion, School of public health, Shahid

Beheshti University of Medical Sciences, , Iran

5 MD, MPH, CDC Manager of Health Deputy, Alborz University of Medical Sciences, ,

Iran

Corresponding author

Hojatollah Barati,

MD, MPH, CDC Manager of Health Deputy, Alborz University of Medical Sciences, Karaj,

Iran

Phone: + 988733131366, Fax: +988733664643

E-mail: [email protected]

Running Title: A Cholera Outbreak Investigation

A Cholera Outbreak Investigation in Alborz Province, Iran: Matched Case-Control Study

Abstract

Objectives: A total of 229 confirmed cholera cases were reported in Alborz province during an outbreak from June to August 2011. This study aimed to identify the potential source of transmission to find suitable interventions.

Methods: Age and sex matched case- control study was conducted during the outbreak. For each case, two control subjects were selected from neighborhood. A case of cholera was defined as a bacteriological confirmed case with signs and symptoms of cholera. This study was conducted from 14 June to August 2011. To analyze the data we calculated Odds Ratio (OR) using logistic regression method.

Results: In this outbreak 229 confirmed cholera cases were diagnosed. Risk factors that had relationship with cholera included the followings: consumption of food that was left out the refrigerator or leftover (OR=3.05, 95% CI:1.72- 5.41), consumption of vegetables and fruits in the past three days (OR= 2.75, 95% CI:1.95-3.89), a history of traveling in the past five days

(OR= 5.21, 95% CI: 2.21- 9.72).

Conclusions: Consumption of vegetables and fruits has remained as an unresolved risk factor for cholera outbreaks in Iran in recent years. To reduce the risk of cholera it is recommended to observe health standards for fruits and vegetables from production to consumption, educate people about hygiene food storage at the time of outbreaks, observing health standards during trips at the time of cholera outbreaks.

Key words: Cholera, Outbreaks, Matched Case-Control study, Iran

Introduction

Cholera is an infectious disease with acute watery diarrhea caused by Vibrio cholerae serogroups O1 and O139. It can potentially cause large epidemics in various countries in the world

[1-4]. This disease, particularly in countries where people has an unfavorable situation, in terms of access to safe water and sanitary toilet, is considered as a serious threat to the public health [5,

6].

In 2007, a total of 177,963 cases were reported to the World Health Organization (WHO) with

4031 deaths, compared to 2006 which showed 25% increase in the number of patients [7, 8]. It is estimated that approximately 3-5 million people are annually infected with cholera and it leads to

100000 -120000 deaths worldwide. Although the cholera case fatality rate is the highest in

Africa, the case fatality rates have been reported less than 1% in Asia in 2002 [9, 10]. In Iran, a large cholera outbreak occurred in 1999 in which more than 10,000 people infected and 109 people died. In another large outbreak in 2006, the number of confirmed cholera in Iran was

1150, of whom 11 people died [11, 12]. Cholera risk factors for outbreaks include poverty, underdevelopment, population density, low education, traveling to high risk area, consumption of leftovers, consumption of unsafe fruits and vegetables [13, 14].

Other risk factors for cholera outbreaks that can be pointed out are sudden changes in hygiene behavior, water and toilet [15, 16]. Natural disasters such as floods can lead to defragmentation of health conditions and cause inadequate health services. Sudden population movement and the seeking refugee may affect water and health resources. It is very important to be aware of the modes of transmission of the disease during outbreaks in any region, according to the particular circumstances of that region [17, 18]. Alborz province in Iran is among the areas that cholera outbreaks occur due to its particular circumstances. The aim of this study, which was concurrent with the cholera outbreaks of Alborz province in 2011, was to determine risk factors associated with cholera illness in order to control the outbreak.

Materials and Methods

To determine risk factors associated with cholera, we conducted age and sex matched case- control. The study was conducted during June 14th continued to August 23rd, 2011. A questionnaire administrated by trained interview was developed that included demographic characteristics, symptoms, potential exposures (related to food, water, personal hygiene, and sanitation). A case was defined as any person suffering from watery diarrhea whose illness was proved in laboratories.

After laboratory confirmation of cholera, we used a questionnaire to collect demographic data as well as other data about exposure to possible risk factors; to complete the questionnaire the cases were interviewed. Interviewers visited the places where each case patient was living and selected the controls from the same neighborhood. Every cases was matched with two controls in terms of age group (within 5 years), sex. Controls and their household members had no history of diarrhea.

Information was collected on 229 cases and 458 controls. All exposure variables were included in the multivariate model unconditional logistic regression if their associated P value under univariate analysis was P < 0.1. We calculated the odds ratios (OR) and 95 % confidence intervals (CIs) associated with the independent variables. We used Stata for analyzing data.

Exact is the default and specifies exact (also known in the literature as Clopper–Pearson) binomial confidence intervals. Data were analyzed using SPSS (IBM Corp. Released 2011. IBM

SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp). Results

The first case of cholera was reported on June 14th, 2011. According to the available data, the outbreak was started on June 14th and continued to August 23rd, 2011. The peak of the outbreak was reported on July 23rd with 22 cases, 229 cases were positive for the Eltor and all cases were Ogawa serotype. Figure 1 shows the epidemic curve for Alborz province.

The mean age of both case-patients and controls was 37 years (1 - 86). Of all, 32.3% of the cases were treated in hospital. Demographic characteristics of cases and controls are shown in Table 1.

The patients with cholera had the following symptoms: vomiting (64.6%), nausea (56.8%), abdominal pain (24.5%), headache (24%), myalgia (37%), watery diarrhea (87.3%), and bloody diarrhea (1.3%). Of all the patients with cholera 67.7% received outpatient services (Table 2).

The water distribution system of the urban area of Alborz province has got an updated systematic chlorination system and during the epidemic, the residual chlorine of both urban and rural areas was released to 0.8 ppm. The status of the water supply was in such a way that indicated cholera dissemination was not possible by the water supply system.

There was no significantly associated in univariate analysis between cholera and people’s contact with diarrhea in the past five days; this group of people were found to be at lower risk of cholera

(OR=1.01, 95% CI: 0.66-1.54); in addition, as shown in Table 3, there was no associations between cholera and eating food from street vendors (OR=0.92, 95% CI: 0.52- 1.62).

In multivariate analysis, the risk factors of cholera outbreaks were as follows: consumption of vegetables and fruits in the past three days, consumption of food that was left out of refrigerator

(leftover), and history of traveling in past five days (Table 4). OR of consumption of vegetables and fruits in the past three days (OR= 2.75, 95% CI: 1.95-

3.89), food that was left out of refrigerator (leftover) (OR= 3.05, 95% CI: 1.72- 5.41), and history of traveling in past five days (OR= 5.31, 95% CI: 2.21- 9.72).

Discussions

According to the results of this case control study, the risk factors of cholera outbreaks were as follows: consumption of vegetables and fruits in the past three days, consumption of food that was left out of the refrigerator (leftover), and a history of traveling in five days ago.

The results of this study about the onset of the epidemic was consistent with other studies [1, 11].

The majority of outbreaks in the country are occurred in warm seasons and summer [1, 19].

There was not any relation between cholera and contact with other cases of diarrhea in the past five days (OR= 1.01, 95% CI: 0.66 -1.54). There is limited evidence indicating the role of family contacts in the transmission of infection, however some studies have found that the presence of a case at home is a risk factor [20, 21] and that family members can spread cholera via touching water and foods at home [22]. According to the results of another study contact with a person with diarrhea had a significant association with cholera outbreak [23].

Multivariate analysis showed that vegetables and fruit consumption was a factor affecting the spread of the disease (OR= 2.75, 95% CI: 1.95 - 3.89). It also showed that patients were exposed to the disease more than the control group 2.75 . A case-control study of a cholera outbreak in

Zambia showed that consumption of raw vegetables was significantly associated with cholera

[17]. In Eshrati et al’s study [11], which was conducted in an outbreak in Arak, Iran in 2005, a total of 16 patients and 32 controls were evaluated using a similar method; according to the results, vegetables consumption was considered as an important risk factor for the transmission of the disease. In a case-control study conducted by Barati et al [1] in 2008, fruits and vegetables consumption was reported as a factor affecting the trend of the disease; moreover in a study by

Rahbar et al [18] consumption of raw vegetables irrigated with wastewater was reported as an effective factor. In another study [15, 24] a significant association was observed between the consumption of vegetables and cholera, which is consistent with our study. Appropriate and timely sampling of vegetables and proper administration of the perchlorate powder to disinfect vegetables may play an important role in the prevention of cholera.

There was no significant associations between cholera outbreak and Purchasing food from street vendors or restaurants (OR= 0.92, 95% CI: 0.52-1.62). In Eshrati`s study, no significant association was found between eating out and cholera [11]. In Mahdavi’s study, no significant associations was found between food consumption in mobile restaurants and the disease [25].

Moreover, in study by Nguyen et al. [24] the results of multivariable analysis showed that street- vended food and drink were not significantly associated with cholera. Eating out was also reported as a risk factor in cholera outbreaks in Uganda and Haiti [26, 27]. In many other outbreaks, the consumption of drinks and foods purchased from street vendors are mentioned as an important risk factor [28, 29]. Street food vending is a possible way of cholera transmission in the population which is similar to findings of Loharikar et al. [30]. The vended items are most likely to be contaminated by environment and poor handling. Epidemiological evidence from

Zambia showed that contaminated food was a major path of transmission of cholera during an outbreak [17]. As a result, the most effective ways to prevent transmission of cholera are the followings: controlling foods from production to distribution and consumption, disinfecting vegetables and fruits, and educating people.

The other risk factor in this outbreak was the consumption of food that was left out of refrigerator (leftover); it had a strong relationship with cholera (OR= 3.05, 95% CI: 1.72- 5.41). Our finding is consistent with Izadi et al’s study [31]. Such a relationship has been also reported in outbreaks in other countries, and in fact a delay between cooking and eating previous V. cholerae with is needed to produce disease [32-34].

In this study, there was a significant association between history of traveling in past five days and cholera outbreak (OR= 5.31, 95% CI: 2.21- 9.72). Compared with the controls, cholera cases traveled more in the past two weeks (P<0.05) [35]. A number of demographic and socioeconomic factors including age, gender, nutritional status, social status, economic status, and history of travelling abroad are also known to play a crucial role in susceptibility to choleragenic V. cholerae. Poor sanitation and low access to health facilities during travel and purchasing food from street vendors or restaurants are among the important factors contributing in cholera. It has become clear that good sanitation and hygienic practices in travel can largely prevent the disease [36-38].

The water supply, distribution and chlorination system of Alborz province is in such a way that makes the cholera dissemination impossible. The water refinery system, water distribution system, water chlorination, daily chlorination monitoring during the cholera epidemic ensure that cholera outbreak is not possible by the water supply system. In recent years, most of the reported epidemics were not because of the water supply problems.

Conclusion

Consumption of fruits and vegetables has remained as an unresolved risk factor for cholera outbreaks in Iran in recent years. To reduce the risk of cholera it is recommended to observe health standards for fruits and vegetables from production to consumption, educate people about hygiene food storage at the time of outbreaks, observing health standards during trips at the time of cholera outbreaks.

Like other case control studies, this study had some limitations. This study was conducted during the outbreak and had not been designed in advance; hence the data might have not been collected comprehensively.

Acknowledgements

The authors would like to thank Alborz University of Medical Sciences, Karaj, Iran for supporting us to conduct this study.

Conflict of interests

No conflict of interests is declared.

References

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Table 1. Demographic characteristics of cases and controls in cholera outbreak in Alborz Province, 2011

Variable Cases (%) Controls (%) P Value* (N= 229) (N= 458)

Sex Male 102 (45) 203 (44) 0.95

Female 127 (55) 255 (55) Age group <10 9 (4) 16 (4) 0.38 10-19 14 (6) 23 (5)

20-39 117 (51) 213 (46) 40-59 68 (30) 173 (38) >60 21 (9) 34 (7) Nationality Iranian 222 (97) 450 (98) 0.26 Afghani 7 (3) 8 (2) residence Urban 215 (94) 430 (94) 1 Rural 14 (6) 28 (6) Marital status Single 58 (25) 121 (26) 0.75 Married 171 (75) 337 (73) Village of residence Main 79 (11) 78 (22) 1

Subsidiary 21 (3) 21 (6) * The proportions of cases and controls were tested via chi square test

1

Table 2. Frequency of sign, severity of diarrhea, and type of treatment of patients with cholera

Sign N (%) (95% CI of %)*

Vomiting 148 (64.6) (58.3 - 70.8)

Nausea 130 (56.8) (50.3 - 63.2)

Fever 51 (22.3) (16.8 - 27.7)

Abdominal pain 56 (24.5) (52.5 - 65.3)

Headache 56 (24.5) (18.8 - 30)

Myalgia 77 (33.6) (27.4 - 39.7)

Severity of diarrhea 35 (15.3) (9.2 - 21.4) Low 73 (31.9) (25.4 - 37.6) Moderate 121 (52.8) (46.8 - 58.3) Severe Type of treatment 74 (32.3) (26.4 - 38.7) Outpatient 155 (67.7) (61.2 - 73.5) Hospitalization * CI, Confidence Interval

2

Table 3. Univariate analysis for selected potential risk factors in cholera outbreak

Variable Cases Controls Crude OR (CI) † P Value N (%) N (%)

Contact with other cases of 25 (10.9) 21 (4.6) 1.01 (0.66 – 1.54) 0.943 diarrhea in the past five days Vegetables and fruits consumption 155 (67.6) 185 (40.3) 3.09 (2.21 – 4.31) 0.0001 the past three days* Purchasing food from street 19 (8.2) 41 (8.9) 0.92 (0.52 – 1.62) 0.774 vendors or restaurants Consumption of food that was left 40 (17.4) 22 (4.8) 4.19 (2.42 – 7.25) 0.0001 out of refrigerator (leftover)* History of traveling in past five 61 (29.7) 28 (6.1) 5.75 (3.44 – 9.02) 0.0001 days*

* P < 0.1.

†Adjusted according age and sex.

†OR=Odds Ratio; CI= Confidence Interval

3

Table 4. Multivariate analysis for selected potential risk factors in cholera outbreak

Variable Adjusted OR (CI) P Value

Vegetables and fruits consumption 2.75 (1.95 - 3.89) 0.0001 in the past three days Consumption of food that was left 3.05 (1.72 - 5.41) 0.0001 out of refrigerator (leftover) History of traveling in past five 5.31 (2.21 – 9.72) 0.0001 days OR= Odds Ratio; CI = Confidence Interval

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Figure1. Epidemic curve of cholera outbreak in Alborz province, 2011.