Context: An outbreak of fever with severe joint pain started in the Palam area of Delhi in August 2010. An entomological and epidemiological investigation of this outbreak was conducted to ascertain the nature and cause of the outbreak. Aim: Aim of the study was to investigate the nature and cause of the outbreak and to contain its further spread. Settings and Design: It was a cross-sectional study conducted in the Palam area of south-west Delhi, situated at a distance of about 20 km from Medical College. It is one of the field practice areas for training of undergraduate and postgraduate students of Department of Community Medicine of Medical College of Delhi. Materials and Methods: All patients attending OPD of Primary Health Center (PHC) Palam, complaining of ever with incapacitating joint pain, were screened for chikungunya fever. Of the 750 suspected chikungunya patients, 130 blood samples were randomly drawn amongst these patients. Out of the 130 tested, 97 (70.8%) were positive for the IgM antibodies against chikungunya virus. House-to-house survey was conducted in the affected area for more cases and to find out the vector-breeding sites. Statistical Analysis: Frequency distributions were calculated for age and sex. Results: The main breeding sites of the mosquitoes were the desert coolers of houses, water stored in metal and plastic containers, and water collections at construction sites. Aedes mosquito was present in almost all the houses surveyed in the area. Conclusions: It was concluded that the routine campaigns need to be organized regularly within the community highlighting the potential breeding grounds of mosquitoes and the possible control methods. Source reduction strategies like cleaning of desert coolers on weekly basis, emptying of water containers, and close monitoring of construction sites for potential breeding of the vector needs to be done on a regular basis to avoid future outbreaks.
Keywords: Aedes mosquito, chikungunya outbreak, entomological investigations
|How to cite this article:
Jain R, Acharya AS, Khandekar J, Jais M. Entomo-epidemiological investigations of chikungunya outbreak in Delhi, India. Ann Trop Med Public Health 2013;6:297-300
|How to cite this URL:
Jain R, Acharya AS, Khandekar J, Jais M. Entomo-epidemiological investigations of chikungunya outbreak in Delhi, India. Ann Trop Med Public Health [serial online] 2013 [cited 2020 Oct 25];6:297-300. Available from: https://www.atmph.org/text.asp?2013/6/3/297/120987
Chikungunya fever is a debilitating, but nonfatal, viral illness that is spread by the bite of infected Aedes mosquito.  Chikungunya infection presents as an acute onset disease characterized by fever, chills, headache, nausea, vomiting, joint pain, and rash. In Swahili, chikungunya means which contorts or bends up. This refers to the contorted (or stooped) posture of patients who are afflicted with the severe joint pain (arthritis) which is the most common feature of the disease. ,,,,, Usually the infection causes no symptoms, especially in children. While recovery from an episode of chikungunya is the expected outcome, convalescent period can be prolonged and persistent joint pain may require analgesic (pain medication) and long-term anti-inflammatory therapy. , Infection appears to provide lasting immunity. The time between the bite of a mosquito carrying chikungunya virus and the start of symptoms ranges from 1 to 12 days. ,
In India, three major epidemics of chikungunya fever have been reported during the last century viz. 1963  in Kolkata, 1965 in Pondicherry and Chennai in Tamil Nadu, Rajahmundry, Vishakapatnam, and Kakinada in Andhra Pradesh, Sagar in Madhya Pradesh, and Nagpur in Maharashtra, and in 1973 in Barsi in Maharashtra. , The disease re-emerged in year 2006 and became epidemic affecting 17 states of the country, starting from the state of Andhra Pradesh, including Delhi, infecting more than 1.39 million people before the end of the year. In 2007, 59,535 cases were suspected of having chikungunya fever. In 2008, the provisional number of cases reported till mid-October was 71,222. ,
In August 2010, several patients complaining of fever and severe joint pain were seen at the out-patient department of Palam Primary Health Center (PHC). In fact, many members of a family simultaneously suffered from similar symptoms characterized by prolonged incapacitation. Keeping a provisional diagnosis of chikungunya fever, we investigated this outbreak of fever with joint pain. Palam is located in south-west part of Delhi. The PHC caters to a population of 1,20,000 in areas pertaining to reproductive and child health and common infectious diseases. Laboratory facilities for diagnosis of common ailments are also available at the center. The center also runs facilities under National Health Programmes for Vector-borne diseases, Tuberculosis, HIV/AIDS, Immunization, and Family planning services.
City had witnessed an outbreak of the fever in year 2006 along with dengue. , In 2010, simultaneous outbreak of fever with joint pain also occurred in the South Delhi area involving parts of Defence colony, Greater Kailash, etc. As dengue and chikungunya infections may present with similar clinical picture, absence of laboratory confirmation makes the exact diagnosis difficult. Thus in the current outbreak with complain of joint pain and fever, laboratory investigations were conducted to confirm the diagnosis. This is also one of the few outbreaks in Delhi where laboratory-confirmed chikungunya cases have been reported from one single community.
We report here findings of a chikungunya outbreak investigation conducted during the period of September to December 2010 in the Palam area of Delhi.
|Materials and Methods|
Suspected chikungunya outbreak started in Palam at the end of August 2010 and first case reported on 28th of August with complain of joint pain and fever. In the subsequent week, 24 more cases reported raising the suspicion of an outbreak of chikungunya. [Figure 1] describes the cumulative occurrence of suspected cases as reported to the PHC Palam and detected during field survey from month of August to December which is the study period. Main areas affected were Palam village, Rajnagar II, and Mahaveer Enclave. On suspicion of the outbreak, both epidemiological and entomological investigations were conducted in the affected area.
|Figure 1: Line diagram showing suspected cases of chikungunya in primary health center Palam, August– December, 2010
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Among all patients coming to OPD of Palam PHC, every 5 th patient with complain of fever and joint pain and also satisfying WHO clinical and/or epidemiological criteria for chikungunya were selected for serological investigation. , The blood samples were tested using IgM ELISA in Microbiology Department of Medical College. ,, These kits were provided to the department by the National Institute of Virology under the National Vector-Borne Disease Control Programme. The test can detect IgM antibodies in blood 3-5 days after the onset of symptoms.
Patients were instructed to come back to the center 5 days after the sample was drawn. Results were conveyed to those tested serologically in the form of a report or conveyed telephonically if the patient or relative did not come back for the follow-up. Result had no bearing on the treatment of patients, as the treatment given was mainly supportive in the form of analgesic.  All suspected patients were asked questions with the help of a semistructured interview schedule regarding presence of day-biting mosquitoes at home or place of work, potential breeding sites, and similar complaints even if milder in the family and neighborhood. After interviewing, the patients were educated about the vector and the disease with the help of flip chart in the center. Health talks on mosquito-borne diseases and especially on dengue and chikungunya were conducted at repeated intervals at the center for all the patients.
House-to-house survey was conducted in third and fourth week of September by a team of doctors in the affected area to check for presence of larva and actual and potential breeding sites in the community. During house-to-house survey, information was collected regarding the presence of more cases with similar complaint of joint pain with fever. During the survey, 54 more cases with similar symptoms in the community were detected. Also, areas in and around the affected houses were surveyed for presence of Aedes mosquito which during periods of inactivity, typically rest indoors, especially in bedrooms, and mostly, in dark places, such as clothes closets and other sheltered sites.  Resting collections were done using mouth aspirators. Containers were examined for the presence of larva. Construction sites were specifically visited as they are known breeding sites for the Aedes mosquito. The team ensured emptying of coolers and containers which had breeding. Also ditches and sites with fresh water collections were filled. Temephos which is 1% abate, an effective larvicide approved for use in water bodies intended for drinking purposes, was added to potential sites wherever necessary.
Simultaneously on receiving the first lab-diagnosed positive case report, Municipal Corporation of Delhi was notified and antilarval and antimosquito measures were intensified in the area.
97 patients out of 137 (70.8%) were confirmed serologically positive for chikungunya virus by IgM Mac ELISA. , Though there was no death reported due to chikungunya, morbidity was quite high. Even after the acute episode of chikungunya fever subsided, joint pain continued for several weeks.  This affected the quality of life of patients and hampered their routine activities.
During the larval and entomological survey, Aedes mosquito was found to be present in the affected area. Presence of vector was compounded by the breeding in construction sites present within 100 m of the houses affected. Breeding was detected with the help of larval survey.
As depicted in [Table 1], 62.8% of those affected belonged to the age group of 15-45 years, two thirds were females, and 56% of those presenting with the complaints reported presence of day-biting mosquitoes in their houses.
|Table 1: Frequency distribution of characteristics of cases of chikungunya
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Breeding was found mostly in water containers made of plastic and metal, desert coolers, and construction sites. House index, Breteau index, and container index were found to be 46.67%, 88.4%, and 12.6%, respectively, which indicated severe risk. See Box no. 1  for definitions of the indices.
During the survey, community was educated about the mosquito-borne diseases with special emphasis on Aedes breeding. Health talks were conducted with the help of flip charts in a group of 2-3 families at a time, throughout the survey period by one of the members of the team. The containers and coolers with breeding were emptied, and people were educated about the necessity of safe water storage practices, emptying of coolers on weekly basis, and being vigilant about the potential sites within the community. They were also educated about the personal protective measures.
Cases started reporting to PHC Palam at the end of August as shown in [Figure 1], with gradual increase in the subsequent months and peaked in October. The number of cases reduced thereafter and tapered down in December. The trend showed similarity with the breeding pattern of the vector Aedes. Outbreaks mostly occur in the post-monsoon period when the vector density is very high. Chikungunya epidemic displays secular, cyclical, and seasonal trends. There is an interepidemic period of 4-8 years (sometimes as long as 20 years). 
Delhi suffered from chikungunya after a gap of 4 years,  which coincided with the disease trend. During the year 2010, Delhi underwent considerable construction activity as a part of preparation for hosting the 2010 Commonwealth Games. Due to irregularities in water supply during this phase, the residents of the affected areas started storing water in containers which were found to be the main site of mosquito breeding. Construction sites in the area also posed considerable threat as both actual and potential breeding sites for the Aedes mosquito.
After the outbreak investigation, it was concluded that in order to prevent recurrence of similar outbreaks in the future, an ongoing process of community education regarding the vector breeding sites and its prevention should be initiated. Medical and health professionals should educate the community about the disease, mode of transmission, control measures, and treatment availability. People should be encouraged to protect themselves from the bite of mosquitoes by using insecticide-treated mosquito nets (LLIN) against mosquitoes.
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