Journal of Marine Medical Society

: 2019  |  Volume : 21  |  Issue : 1  |  Page : 31--35

An epidemiological study of varicella outbreak in a military training establishment

Dattatraya Ramkrishna Sinalkar1, Rahul K Ray2, SM Sudumbrekar3,  
1 Department of Community Medicine, Station Health Organisation Portblair, Andaman and Nicobar Islands, India
2 Department of Community Medicine, Head Quarters, Central Command, Lucknow, Uttar Pradesh, India
3 Department of Neurosurgery, Command Hospital Southern Command, Pune, Maharashtra, India

Correspondence Address:
Col Rahul K Ray
Community Medicine, Head Quarters, Central Command, Lucknow, Uttar Pradesh


Context: Though incidence of the Varicella has decreased in recent years due to introduction of vaccine; outbreaks continue to occur in closed environments such as those of militaries. The present study describes one such outbreak in a military training establishment. Setting and Design: This cross sectional study was conducted at a Secondary level hospital. Aims: To describe the distribution and characteristics of Varicella infections and to make suitable recommendations for prevention and control. Materials and Methods: All admitted cases of Varicella from a military training establishment during the outbreak were included in the study. Epidemiological data was collected by face to face interview. Statistical Analysis Used: Statistical analysis was performed using Epinfo software version 3.5.3. Results: Total 332 recruits were admitted in the local military hospital in said outbreak. Eight administrative staffs of recruiting center and two medical staffs attending the patient at hospital were also affected. The age of the patients ranged from 18 to 34 years with a mean of 20.3 ± 3.5 years. None of the cases admitted had developed any complication and their hospital stay remained uneventful. Maximum cases (59%) were presented with rash as a first clinical manifestation and 94.3 % of them had history of contact with a case of Varicella. None of them gave a history of vaccination. Conclusions: Though policy to offer vaccination against Varicella to all recruits on entry level exists, it should be implemented on ground to ensure unnecessary interruption in training activities.

How to cite this article:
Sinalkar DR, Ray RK, Sudumbrekar S M. An epidemiological study of varicella outbreak in a military training establishment.J Mar Med Soc 2019;21:31-35

How to cite this URL:
Sinalkar DR, Ray RK, Sudumbrekar S M. An epidemiological study of varicella outbreak in a military training establishment. J Mar Med Soc [serial online] 2019 [cited 2020 Mar 29 ];21:31-35
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Varicella Zoster virus causes varicella among susceptible population and is characterized by pruritic vesicular rash, fever, headache, and malaise.[1] Incubation period ranges from 10 to 21 days. Patients are infectious 1–2 days before the appearance of rash until all lesions are crusted.[2] The virus spreads mainly by respiratory route by direct contact of susceptible personnel with cases.[3] Secondary attack rate among susceptible contacts ranges from 65% to 86%.[1],[4],[5]

Outbreaks of chickenpox in a military training center affect a considerable number of military recruits, leading to a number of hospital admissions and have an adverse effect on training activities.[6]

Outbreaks get reported quite often in countries like India where vaccination is not part of the country's national immunization policy. Varicella outbreaks occur frequently in closed and crowded environments such as military barracks through aerosol spread.[7] Severity and complications are common among adults.[8] Secondary bacterial infections, dehydration, pneumonia, encephalitis, and cerebellar ataxia are few severe complications which may result in death. Hence, varicella is an important health issue among military personnel.[4],[9],[10]

An outbreak of varicella occurred among personnel of a training establishment. All cases were admitted to the nearest military hospital. Based on the information obtained from an inbuilt health intelligence (HI) surveillance section of station health organization and hospital authorities, investigation and control measures were initiated.

The recruits undergo training over a period of 12–18 months.

This study was carried out to describe the distribution and characteristics of varicella among personnel and to make suitable recommendations for the prevention and control of outbreak in a military training establishment.


Study setting

This was a cross-sectional study carried out in a secondary care hospital. All varicella cases from the training center who were admitted to the hospital during outbreak were included in the study. Cases started occurring while the recruits were in the first phase of their training. Many contacts of index case developed disease over subsequent days and were admitted.

All cases were interviewed on the day of admission by trained health personnel after informed consent. Data was collected by means of a semi-structured questionnaire based on the study objectives. The data included personal details, clinical features including travel history, movements for camps/outdoor training, and immunization details. An epidemiological case sheet and line listing was done. Contact tracing was carried out for close contacts.

Data thus collected were analyzed using Epi-info software version 3.5.3 (Centers for Disease Control, Atlanta, United States of America) and IBM SPSS Statistics for Windows version 24 (IBM Corp., Armonk, NY: USA). Secondary attack rate was calculated by dividing the number of cases with the number of susceptibles within the incubation period of index case.

Case definitions

Clinical case was defined as the one with acute onset of diffuse (generalized) maculopapular vesicular rash with fever among personnel in a training establishment admitted in local military hospital with no prior history of varicella.[11] The case definition was based only on the clinical diagnosis, and the cases were not laboratory confirmed.

Probable case was the one that meets the clinical case definition and was not epidemiologically linked to another probable or confirmed case.[11]

Confirmed case was the one that meets clinical case definition and was epidemiologically linked to another probable or confirmed case.[11]

Outbreak was confirmed by comparing the weekly incidence of varicella with similar period of previous 3 years' data as available in the establishment.

Close contacts were defined as recruits/personnel who had direct contact indoor or outdoor, defined as being within a distance of <1 m from a case and/or had discussion of more than three words with a case and/or had face-to-face contact with the case.

Susceptibles were those recruits/personnel with no known history of varicella or vaccination against varicella and who came in close contact with cases.

Overcrowding was defined using the American Public Health Association Centers for Disease Control and Prevention criteria.[12] Maximum occupancy of any dwelling unit/room should not exceed lesser than the requirements of the first (at least 150 sq. foot floor area) and the second and subsequent occupants (at least 101 sq. foot floor area). If dwelling of two or more rooms was occupied, then it should have at least 70 sq. foot of floor area for the first occupant and at least 50 sq. foot floor area for subsequent occupants.

Control measures

All close contacts were immediately quarantined in separate accommodations/temporary tents. Separate messing facilities and training facilities were established for segregated recruits. Awareness drives were conducted for instructional staff for sensitizing the recruits about the importance of frequent handwashing, cough etiquettes, use of face mask, restriction of movement, avoiding mass gathering, to increase space between beds, head-to-toe pattern of sleeping, wet mopping of floors, early reporting of symptoms, etc. Additional tents were established for accommodating recruits. Personnel with a previous history of varicella were tasked for taking care of quarantined recruits. Vaccination of all recruits was initiated after availability of vaccine. Vaccination was initially given to close contacts; health personnel and subsequently all recruits were vaccinated in batches. Surveillance was continued till next four weeks after the last case was diagnosed.


A total of 342 cases of varicella from a military training center were admitted in the Military Hospital during the study period. Out of these, 332 (97%) were young recruits, eight (2.4%) were administrative staff and two (0.6%) were medical staff of the center attending the patients.

Overall attack rate among the recruits during this outbreak was 4.8%, whereas the corresponding attack rates of the last 3 years were 0.5%, 1.5% and 0.8% respectively.

An epidemic curve for time distribution of cases was prepared, which showed that 22 cases occurred within the incubation period of the index case which later propagated the disease among the other recruits [Figure 1]. In our study, out of 26 susceptible recruits, 22 recruits had developed the disease. Secondary attack rate was found to be 87% among susceptible close contacts.{Figure 1}

Subunit-wise distributions of the admitted recruits are shown in [Figure 2] and [Figure 3]. In our study, attack rate was maximum (5.3%) among recruits of Subunit III. The Subunit II had attack rate of 4.4%, while the same for Subunit I was 3.9%.{Figure 2}{Figure 3}

As shown in [Table 1], the most common clinical manifestation observed among cases was rash (100%) followed by fever (83%) and body ache (36%). The first site of appearance of rash was the trunk in the majority (85%) of the patients. Maximum cases (59%) had presented with rash as a first clinical manifestation, whereas fever was the first clinical manifestation in 40% of cases. Nearly 94.3% of the patients (confirmed cases) had a history of contact with a case, whereas 5.7% of the patients (probable cases) were not known to have any contact with any case. None of them gave a positive history of varicella infection and vaccination against varicella in childhood. None of the cases developed any complications and recovered completely from the disease. The age of the patients ranged from 18 to 34 years, with a mean of 20.3 ± 3.5 years. The mean hospital stay of the cases was 8.4 days, with a standard deviation of 1.4.{Table 1}

Overcrowding was observed in the barracks with corresponding reduction in available floor area per recruit. Area available per recruit was only 36.5 sq. feet.

As shown in [Figure 1], the number of cases steadily increased from M Month to M+3 Month and then started to decline. After M+5 month, the number of cases was at preoutbreak level.

Epidemiological linkage between the cases was studied and is depicted in [Figure 4].{Figure 4}


In the present outbreak, the index case was a recruit of 18 years with 15 days of military service. He had traveled in train from North to South along with two other newly selected candidates from the same Army Recruiting Office (ARO). All of them had contact with a co-passenger in the train who had varicella. Soon after reporting to the center, they were accommodated in the barracks along with other recruits from various AROs. All of them had developed varicella subsequently and were admitted to the hospital. These recruits in turn had spread the disease to their close contacts in the barracks. After one month of the initial phase, the recruits were transferred for trade-wise training to different subunits as per their trades and relocated to the respective subunits' accommodation.

The epidemic curve demonstrates a propagated epidemic, with multiple peaks indicating transmission of infection to successive clusters of recruits. The interval between the peaks was less than the incubation period of varicella (10–21 days), which implies that cases were infectious during the incubation period.

All the newly inducted recruits were sheltered in same barracks. This led to overcrowding and compromise in the ventilation and hygiene sanitation of recruits. Furthermore, mixing of recruits in the classes, dining halls, sports ground, and auditorium prior to the implementation of preventive measures resulted in the further spread of varicella.

Almost all quarantined close contacts were deployed as working parties along with other recruits for the preparation of incoming major event to be held in the first half of fourth month of reporting of recruits. This deployment was from last week of third month and first week of fourth month at various locations of the center. This defeated the purpose of segregation and resulted in multiple peaks of cases in epidemic curve and was an important cause for prolongation of an ongoing epidemic.

Known high secondary attack rate of disease also contributed to the spread. The secondary attack rate in our study (87%) was comparable with that of other studies.[4],[5]

Another reason for spread among the recruits was transmission occurring among close contacts during the period of infectivity, especially the period of communicability extending 1–2 days before the onset of rash.[3] None of the close contacts were either vaccinated or had any previous infection with varicella.

Being winter season, lower temperature might have accelerated the transmission of varicella among susceptible recruits as seen in the study conducted among mobile troops by Chatterjee et al.[13],[14]

This outbreak occurred among military recruits residing in close proximity, making them vulnerable to the spread of highly communicable diseases like varicella. A similar outbreak was also reported among military troops at Singapore.[7]

Limitations of the study

Laboratory confirmation of cases and serosurveillance among the recruits for determining the immunity among close contacts could not be carried out due to lack of laboratory facility in the study area.


This outbreak of varicella in a military training center affected young recruits coming from various parts of the country leading to their hospital admission and an adverse effect on training activities.

Overcrowding, higher secondary attack rate of varicella among susceptibles, no history of vaccinations prior to entry, nonavailability of vaccines at the training center for administration to recruits on entry, and deployment of segregated recruits for the preparation of incoming major event by executive authorities despite medical advice have played a supportive role in the transmission of varicella.

Early initiation of preventive measures as advised by medical authorities is of paramount importance. Executive authorities should strictly institute the measures as advised. Permanent solution for reducing the overcrowding may be considered by increasing the infrastructure for recruits. Occurrence of even a single case of varicella has the potential of rapid spread among recruits and outbreak, and hence, vaccination of all recruits on entry on the very 1st day of reporting to the training center should be considered to prevent such outbreaks in future.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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