Prevalence of chikungunya in the city of Ahmedabad, India, during the 2006 outbreak: A community-based study Tapasvi Puwara#, Jay K. Shetha, Vijay Kohlib and Rajpal Yadavc a
Department of Community Medicine, Smt. Nathiba Hargovandas Lakhmichand Municipal Medical College, Ahmedabad, Gujarat, India b
Department of Health, Ahmedabad Municipal Corporation, Ahmedabad, Gujarat, India c
National Institute of Malaria Research (ICMR), Field Unit, Nadiad, Gujarat, India
Abstract Prevalence of chikungunya in the city of Ahmedabad, India during the 2006 outbreak was investigated to estimate the prevalence of suspected chikungunya cases to find out demographic parameters and proportion of various symptoms among suspected chikungunya cases, and to evaluate the effectiveness of control measures implemented by the public health sector. A total of 6667 people from 1301 households were surveyed. The prevalence of suspected chikungunya cases was 32.9% (31.8% – 34.2%). Prevalence was higher in females (p<0. 006), and also highest for the age group of 40 to 80 years. The north zone of the city, a densely populated slum, had significantly higher (p<0.001) numbers of suspected cases than the other zones. Case numbers were significantly higher in slums than in more affluent settings such as apartments and bungalows (p<0.001). Chills, headaches, joint swelling and itching were the main symptoms reported by the majority of cases. The majority (67.6%) of suspected cases sought treatment from the private sector and another 8.5% received no treatment at all. The hospitalization rate was found to be 6% for the study. Among mosquito control measures, visits by health workers (73.4%), application of larvicides (67.5%) and fogging (42.4%) achieved good coverage compared with information education and communication (IEC) measures (28.3%) and other activities. Keywords: Chikungunya; prevalence; India; community-based study; disease burden.
Introduction Chikungunya fever is an arboviral disease transmitted to humans by infected mosquitoes of the Aedes genus.[1] Since the first isolated #
incident in Tanzania in 1952, [2] several outbreaks of the disease, caused by this alphavirus have been documented throughout South-East Asia.[3-6]
E-mail: drtapasvi@gmail.com
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During an acute attack of chikungunya, patients usually develop a sudden onset of fever, headache and arthralgia[7] after an incubation period of 2–4 days (range 3–12 days). Symptoms are generally self-limiting and last for 2–3 days. However, arthralgia may persist for months or years.[1] During the last outbreak in India and other South-East Asian countries, the epidemic spread rapidly and affected many communities with an attack rate as high as 40%–60%.[8] Chikungunya re-emerged in India in December 2005 after a gap between epidemics of 32 years.[9] This particular outbreak was caused by the central/east African genotype[10] and infected around 1 400 000 people in India during 2006. It was estimated that some areas had attack rates of 45%.[11] Official figures from the government of India indicated that 1.39 million suspected chikungunya cases were identified from 152 districts.[12]
a suspected case was modified and any person having acute fever and joint pain any time during the past one month was considered a suspect chikungunya case for the purpose of the study. Symptoms were reported as perceived by the individual personally or by the reporting adult family member in case the member was not available for the interview. The study was carried out using a standard questionnaire, pre-tested two weeks before the study. The questionnaire also included information on treatment-seeking practices, knowledge of prevention and control, as well as activities carried out by the local health department. All investigators for the study were trained for one day in how to identify a suspected case of chikungunya as per the adopted definition and how to fill in the questionnaire as per the study format. Senior faculty from the Municipal Medical College of the city checked every form at the end of each day and verified the information with investigators. Pre-testing of the questionnaire was done in the field on 612 people. The sample size was calculated on the basis of a pilot study which estimated the case prevalence to be greater than 30%. The sample size in the current study exceeds the requirement several-fold. The city of Ahmedabad is divided into five administrative zones and 43 wards. In an effort to make the sample selection representative of the entire city population, 30 houses were selected randomly from each ward irrespective of presence of suspected case. As more than 40% of the population of the city resides in slums, half of the houses in each ward were selected from slums while remaining half were selected from other localities including bungalows and apartments.
Materials and methods The present study was conducted in Ahmedabad city during September 2006. A house-to-house survey was done to search for suspected chikungunya fever cases and collect information about reported symptoms. A definition of a suspect case was adopted from the Communicable Disease Alert (CD Alert) issue, Vol. 10 (2) of February 2006 published by the National Institute of Communicable Diseases (NICD), Delhi.[13] It defined suspected chikungunya as “…an acute illness characterized by sudden onset of fever with several of the following symptoms: joint pain, headache, backache, photophobia, arthralgia and rash”. This study was conducted during the peak of the outbreak confirmed by the National Institute of Virology (NIV), Pune, during April 2006. Therefore, the definition of
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Limitations of the study The study’s case definition was based entirely on self-reported cases. It was not feasible to do confirmatory serology tests for each and every self-reported case. Self-reported cases were also not cross-examined by medical persons. However, the questionnaire was filled in by intern doctors for each suspected case.
Table 1: Gender-wise distribution of suspected chikungunya cases Gender Male Female Total Suspected chikungunya 1090 1106 2196 Total population 3467 3200 6667 Percentage 31.4 (29.4–32.6) 34.6 (33.4–36.6) 32.9 (31.8–34.2)
Results A total of 1301 houses were surveyed covering a population of 6667. The prevalence of fever over the past one month was found to be 51.3% while the prevalence of joint pain was 41.7%. The prevalence of suspected chikungunya cases was found to be 32.9% (95% CI, 31.8–34.2). Table 1 shows the number of suspected cases was significantly higher in females (Chi square test: 7.35, p=0.006).
Figures in brackets suggest upper and lower limits at 95% confidence interval.
The mean age among suspected cases was found to be 33.7 years. Average family size was 5.17 and the average number of suspected cases per family was 1.7. The agewise distribution of cases reveals the highest number of cases to be in the 20–30 years age group. However, age-specific prevalence rates clearly indicate an increase in the prevalence
Figure 1: Age-wise distribution of suspected chikungunya cases and age-specific prevalence rate 600 50 45
Number of suspected chikungunya cases
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40 35 30
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Suspected cases Age-specific prevalence rate (%)
200
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rate with increase in age. The highest agespecific prevalence rate of 44.4% was in the age group of 60–70 years as shown in Figure 1. The distribution of suspected cases by zone indicates a significantly higher number of cases from the north zone, which is densely populated and a reported starting point of the outbreak in Ahmedabad City. A comparison of house types revealed that a higher number of cases were from slums than others (Chi square test: 15.75, p<0.001). A variety of signs and symptoms were also reported during the household survey, the result of which is shown in Table 2. Table 2: Prevalence of various reported signs and symptoms Signs and symptoms Headache Chills Itching Joint swelling (oedema) Tenderness (palms/ soles) Rashes Oral ulceration Lymphadenopathy N = 2196 1002 974 629 612 602 416 256 18 Per cent of suspected cases (%) 46 44 29 28 27 19 12 1
the population was acutely suffering from suspected chikungunya during the survey. An acute case of suspected chikungunya was taken as having signs and symptoms of suspected chikungunya in the last four days prior to the survey. Table 3 shows the activities carried out by the local health department during the last seven days as perceived by the family respondents. Table 3: Activities carried out by the local health department during the 2006 outbreak Activities Visit by any worker in the last seven days Larviciding of Abate* Fogging General information, education and communication activities Pamphlet distribution Knowledge about how chikungunya spreads Houses where mosquito repellents had been used in the past one month Per cent of houses covered (%) 73.4 67.5 42.4 28.3
17.8 53.7 58.0
*Abate: a larvicide that controls aquatic stages of vectors.
Analysis of treatment-seeking behaviour shows that the majority (67.6%) of cases sought treatment from private facilities; around 23% sought treatment from public facilities, while 8.5% sought no treatment. Over-thecounter drugs were used by 1% of suspected cases for their symptoms while 6% of cases required hospitalization. Three per cent of
Prevention and control activities including the visit by a worker for awareness, release of larvicides (Abate), and fogging and pamphlet distribution, were carried out extensively as a matter of priority for the local health department. Health workers were able to reach the majority of houses for prevention and control activities. Table 3 shows that 53.7% of respondents had accurate knowledge
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or information regarding the spread of the chikungunya disease, while 58.0% of houses had used mosquito repellents in the past month.
Discussion During the 2006 chikungunya epidemic in India there was a controversy over the reported numbers of people affected by the disease. Many newspaper articles and nongovernmental organizations (NGOs) expressed skepticism about the numbers of chikungunya cases reported by the government. [14] The study also identified that the majority of suspected cases sought treatment from the private sector which could possibly explain the lower prevalence reported by the government officials. This communitybased study found that in 2006–2007, the prevalence of suspected chikungunya in the Ahmedabad city was 32.9% (95% CI, 31.8-34.2). The study also revealed that a greater number of females suffered than males, and that those affected were from an older age group, with the highest age-specific prevalence rate being 60–70 years. The north
zone had a significantly higher number of cases, which can be explained by the density of the population and the living conditions prevailing in that zone. Similarly, a favourable environment and lack of protective measures against the vector mosquito might have lead to a higher number of cases in slums compared with other housing types. The hospitalization rate in the study indicates that only 6% had a severe attack of the disease during the 2006 epidemic. The local health department made significant efforts to cover large numbers of houses and families for prevention and control activities. However, more studies using laboratory confirmation are needed to determine the prevalence of confirmed cases of chikungunya.
Acknowledgements We sincerely thank the Ahmedabad Municipal Corporation and the Government of Gujarat for all the support they provided to carry out the study. We also like to thank faculty and intern doctors of Municipal Medical College, Ahmedabad. We appreciate the support given by scientists and staff members of the National Institute of Malaria Research (ICMR), Field Station, Nadiad, Gujarat.
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[4] Sergon K, Njuguna C, Kalani R, Ofula V, Onyango C, Konongoi L, Bedno S, Burke H, Dumilla AM, Konde J, Njenga MK, Sang R, Breiman RF. Seroprevalence of Chikungunya virus (CHIKV) infection on Lamu Island, Kenya, October 2004. American Journal of Tropical Medicine and Hygiene, 2008, 78: 333–337. [5] AbuBakar S, Sam IC, Wong PF, MatRahim N, Hooi PS, Roslan N. Reemergence of endemic chikungunya, Malaysia. Emerging Infectious Diseases, 2007, 13: 147–149. [6] Halstead SB, Udomsakdi S, Singharaj P, Nisalak A. Dengue chikungunya virus infection in man in Thailand, 1962–1964. III3. Clinical, epidemiologic, and virologic observations on disease in nonindigenous white persons. American Journal of Tropical Medicine and Hygiene, 1969, 18: 984–996. [7] Borgherini G, Poubeau P , Staikowsky F, Lory M, Le Moullec N, Becquart JP, Wengling C, Michault A, Paganin F. Outbreak of chikungunya on Reunion Island : early clinical and laboratory features in 157 adult patients. Clinical Infectious Diseases, 2007, 44: 1401–1407. [8] World Health Organization. Chikungunya in India. 2006. Available from: URL: http://www. who.int/csr/don/2006_10_17/en/index.html. [9] Saxena S, Singh M, Mishra N, Lakshmi V. Resurgence of chikungunya virus in India: an emerging threat. Euro Sur veillance , 2006.11(8):E060810.2. [Online] 2006. [Cited 5 February 2007] Available from: http:// www.eurosurveillance.org/ew/2006/060810. asp#2.
[10] Yergolkar PN, Tandale BV, Arankalle VA, Sathe PS, Sudeep AB, Gandhe SS, Gokhle MD, Jacob GP, Hundekar SL, Mishra AC. Chikungunya outbreaks caused by African genotype, India. Emerging Infectious Diseases, 2006,12:1580–3. [11] Outbreak and spread of chikungunya. Weekly Epidemiological Record, No. 47, 2007, 82: 410. Available from http://www.who.int/ wer/2007/wer8247.pdf. [12] National Vector-Borne Disease Control Programme, Government of India, 2006. Available from http://www.nvbdcp.gov.in/Doc/ Facts%20about%20Chikungunya17806.pdf. [13] Chikungunya Fever. CD Alert, Monthly Newsletter of the National Institute of Communicable Diseases , 2006, 10(2):6. Available from http://nicd.nic.in/cdalert/ February-06.pdf. [14] Mavalankar DV, Shashtri P, Raman P. Chikungunya epidemic in India: A major public- health disaster. The Lancet Infectious Diseases, 2007;7;306-7 Available from http:// www.thelancet.com/journals/laninf/article/ PIIS1473-3099(07)70091-9/fulltext#article_ upsell.
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