Epidemiologic lessons: Chickenpox outbreak investigation in a rural community around Chandigarh, North India

Mini Pritam Singh; Gagandeep Singh; Amit Kumar; Amarjeet Singh; Radha Kanta Ratho

doi:10.4103/0377-4929.91497

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ORIGINAL ARTICLE

Year : 2011 | Volume : 54 | Issue : 4 | Page : 772-774

Epidemiologic lessons: Chickenpox outbreak investigation in a rural community around Chandigarh, North India

Mini Pritam Singh¹, Gagandeep Singh¹, Amit Kumar¹, Amarjeet Singh², Radha Kanta Ratho¹
¹ Department of Virology, School of Public Health, PGIMER, Chandigarh, India
² Department of Community Medicine, School of Public Health, PGIMER, Chandigarh, India

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Date of Web Publication

6-Jan-2012

Abstract

Purpose: Primary infection with Varicella Zoster virus (VZV) leads to Varicella or chickenpox. The epidemiology of Varicella has changed dramatically since the introduction of the Varicella vaccine in 1995. The routine childhood immunization in a few countries in the western world like Germany and the United States has reduced the incidence of the disease, associated complications, hospital admissions and deaths related to its complications. However, chickenpox outbreaks are common in naive unvaccinated communities in India. Materials and Methods: We report an outbreak of chickenpox that occurred in a village situated on the outskirts of Chandigarh city in North India in the winter of 2007. The outbreak was confirmed by the detection of VZV IgM by enzyme-linked immunosorbent assay (ELISA) on serum samples from the patients. In patients showing active lesions, Giemsa and indirect immunofluorescence was carried out on scrapings from vesicular lesions. Results: A total of 162 cases occurred in the present outbreak. The serum samples were collected from 20 patients, and all of them showed positive serology for VZV IgM antibodies while 19 showed a positive VZV IgG result by ELISA. The scrapings were collected from two patients showing active lesions, and both were positive by the Tzanck smear examination, and VZV antigen could be demonstrated by immunofluorescence. Conclusions: There is an urgent need to identify naive communities and unvaccinated individuals at risk. Also, there is a need for regular training programmes of health workers posted in peripheral centers so that highly contagious communicable diseases can be picked up in time and such outbreaks can be prevented.

Keywords: Chickenpox, epidemiology, outbreak

How to cite this article:
Singh MP, Singh G, Kumar A, Singh A, Ratho RK. Epidemiologic lessons: Chickenpox outbreak investigation in a rural community around Chandigarh, North India. Indian J Pathol Microbiol 2011;54:772-4

How to cite this URL:
Singh MP, Singh G, Kumar A, Singh A, Ratho RK. Epidemiologic lessons: Chickenpox outbreak investigation in a rural community around Chandigarh, North India. Indian J Pathol Microbiol [serial online] 2011 [cited 2023 Nov 29];54:772-4. Available from: https://www.ijpmonline.org/text.asp?2011/54/4/772/91497

Introduction

Varicella is a highly contagious disease caused by Varicella Zoster virus (VZV). The disease is usually benign in immunocompetent children but can be life-threatening in adults and immunocompromised individuals, with an attack rate approaching >85% after exposure. ^[1],[2] Humans are the only known hosts for this virus, which exists as only one recognised serotype. Viral shedding occurs from the nasopharynx via droplets and aerosols and also from the skin lesions. The incubation period of the disease is usually 14-16 days. The contagious period starts 1-2 days before the appearance of the exanthem and lasts till all the vesicles have crusted, usually within 5-7 days. ^[1]

The incidence of Varicella in temperate climates is 13-16 cases per 1000 people per year, ^[3] and is highest in children aged 1-9 years old, although an increased incidence has been observed in children younger than 5 years due to attendance at child care centers. By contrast, in tropical countries like India, the incidence of Varicella is higher in adults. ^[4],[5] Authors ^[6] have postulated the concept of epidemiologic interference by the high prevalence of certain childhood viruses in the developing countries; the interference is said to postpone the age of Varicella infection. In both temperate and most tropical climates, the incidence of Varicella shows pronounced seasonality, with peaks occurring in the cooler months during winter or spring. ^[7] In temperate climates, epidemics of Varicella have been reported to occur every 2-5 years. The overall case fatality rate in developed countries is 2-4 per 100,000 cases, with the risk of death being highest at the extremes of age. The rate of hospital admission for all ages is 2-6 per 100,000 population, with most admissions occurring in children. ^[8]

Materials and Methods

Nature of the Sample

The outbreak investigation was initiated in the December of 2007, when a number of cases of chickenpox were reported from a village Chandsoli, under the Primary health center (PHC), Ambli, District. Ambala of the state of Haryana in India. All these cases were examined for the presence of typical rash of Varicella. Detailed history was taken and line listing of cases was performed. Blood samples were collected from 20 representative cases of suspected chickenpox infection (in acute or recovery phase) and also from 15 asymptomatic controls in the same community after obtaining written informed consent from the adults and parents (in case of children).

Laboratory Diagnosis

The serum was separated and stored at -20°C till tested for VZV IgM and IgG by ELISA (Euroimmun, Lubeck, Germany). In addition, vesicular scrapings were collected from two patients with active lesions showing vesicles. The slides were prepared for Tzanck smear and stained by Giemsa stain. Indirect immunofluorescence was carried out using VZV-specific monoclonal antibodies (Novocastra, Newcastle on Tyne, UK). ^[9]

Results

Of the 20 representative cases, 14 were children and six were adults (mean age = 13 years). Among these, 11 patients were male and nine were female (M:F ratio 1.2:1). All the 20 suspected cases showed positive serology for VZV IgM antibodies while 19 showed a positive VZV IgG result by ELISA. Active lesions were seen only in two patients, both were positive by Tzanck smear examination, and VZV antigen could be demonstrated by immunofluorescence. No severe complications were observed in children and adults in this outbreak. Five controls were positive for VZV IgG antibodies and gave a history of a past infection with chickenpox.

The detailed history revealed that the index case was a 24-year-old woman who had delivered a baby boy 10 days back. Her husband visited the PHC and described her lesions to the doctor on duty, which typically conformed to that of chicken pox. Anticipating that the mother might transfer the infection to her new born baby, the doctor paid a home visit, confirmed the diagnosis and put her on treatment with acyclovir. He took a detailed history and found that a child with chickenpox in the neighbourhood used to regularly visit them and was the probable source of infection for the lady. The child when questioned revealed that majority of the children taking tuitions with him had a similar disease. The doctor further traced as many children as possible to find out the probable source of this outbreak. On compiling the data, it was found that the tutor of these children, a 20-year-old female had suffered from chickenpox a month ago. The tutor had initially visited a local female health worker to get the lesions examined but the latter failed to diagnose the disease. In spite of having active lesions, the tutor continued to take regular classes of almost 35 children of the village, thereby affecting a majority of them. This tutor in turn had acquired the infection from her elder brother who was a college student in a neighbouring town of Narayangarh. He distinctly remembered that one of his classmates in college had chickenpox and that he had acquired it from him. A complete surveillance was done of the whole village and the surrounding areas of Buddakhera, Jeoli and Shakarpura villages to identify all the active and healed cases of chickenpox. Approximately 162 cases were picked up among a population of 7393, in which majority of the cases were males (62.3%), with a mean age of 11.6 years (range 18 months to 35 years).

Discussion

The present study highlights the epidemiological factors contributing to an outbreak of chickenpox. A perfect setting for the spread of infection was available in the form of ambient temperature in winters and people in a naive community living in close proximity, which lead to the rapid transmission of the virus. When investigated, all the 20 suspected Varicella cases showed positivity for IgM antibody, and 19 were also positive for VZV IgG antibody. This may be due to the fact that by the time the outbreak was diagnosed, most of the patients had healed lesions of duration of about 1-2 months. The only patient who was IgG negative had a history of fever and rash for 4 days. Hence, although she was positive for IgM antibodies, IgG antibody response would not have developed by this time. The present outbreak of chickenpox occurred in early winter, which is the usual time of occurrence. It has been proposed that the transmission potential of the VZV virus might be adversely affected by a combination of high ambient temperatures and humidity in tropical regions. ^[10]

The usual epidemiology of any outbreak follows a typical tree-like pattern, where one case acts as a source of infection to only a few persons. The most unusual pattern in the present outbreak was that a single patient, the tutor of the village, helped in spreading the infection to a majority of the cases [Figure 1]. All cases from that village had directly or indirectly been infected by a child who had attended tuitions thus signifying the tutor's role. The outbreak could have been timely prevented if the health care worker had diagnosed the disease when the tutor presented for clinical examination.

Figure 1: Possible epidemiological linkage of the chicken pox outbreak in the village of Chandsoli

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Vaccination against chicken pox is not recommended in the Indian Universal Immunization Programme. However, the Indian Academy of Pediatrics suggests that it can be given to (a) adolescents who have not had Varicella in childhood, (b) household contacts of immunocompromized children, (c) children attending crèches and day care centers and (d) susceptible adolescents and adults if they are working in the institutional set up, e.g. school teachers, day care center workers, military personnel, health care professionals, etc. ^[11] Studies have shown that the Varicella vaccination when used as post-exposure prophylaxis in children within 5 days of exposure significantly reduces the chance of developing clinical Varicella infection. The effect is more pronounced if vaccine is given within 3 days of exposure, and prevents nearly all cases of moderate to severe Varicella. ^[12] In the current setting, the screening and vaccination of Varicella IgG-negative individuals, once a primary case was identified, would have helped to curtail the outbreak. Also, there is need for regular training programmes of health workers posted in peripheral centers so that highly contagious communicable diseases can be picked up in time and such outbreaks can be prevented.

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