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MILITARY MEDICINE - ORIGINAL ARTICLE
Year : 2018  |  Volume : 20  |  Issue : 1  |  Page : 38-43

An outbreak of varicella among troops on the move: A challenge in field epidemiology


1 Department of Community Medicine, Armed Forces Medical College, Pune, Maharashtra, India
2 HQ 3 Corps (Medical Branch), C/o 99 APO, India
3 Regimental Medical Officer, C/o 99 APO, India
4 Medical Specialist, Indian Level III Hospital, UN Mission in South Sudan
5 Consultant Pathology, Command Hospital Southern Command, Pune, Maharashtra, India

Date of Web Publication9-Jul-2018

Correspondence Address:
Col Kunal Chatterjee
Department of Community Medicine, Armed Forces Medical College, Pune - 411 040, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jmms.jmms_10_18

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  Abstract 

Background: Military population, by virtue of peculiarities of service conditions, such as congregation in living barracks or during exercises present a vulnerability to spread of contagious diseases. Institution of control measures during outbreaks becomes a challenge in Field areas due to operational commitments. The present paper highlights an outbreak investigation conducted in field and some lessons learnt. Methods: This investigation was conducted among troops who had arrived at a new location and soon after took part in training and area familiarisation and among whom chicken pox occurred. Constant troop movement resulted in challenges to institute control measures, which had to be tailored to suit the situation. Aggressive intervention measures such as segregation, contact tracing and strict surveillance resulted in control of the outbreak. Results: A non-immunised military population reported its first two cases during travel in military special train to the battalion's new location. Subsequently cases kept occurring over two months and the constant movement of troops propagated the outbreak, resulting in total of twenty cases. Timely prevention measures successfully broke its runaway nature and controlled the outbreak. Conclusion: Early identification of cases and aggressive intervention measures were successful in effective control of outbreak.

Keywords: Chicken pox, mobile troops, outbreak


How to cite this article:
Chatterjee K, Kunwar R, Taneja G, Mitra S, Srinivas V. An outbreak of varicella among troops on the move: A challenge in field epidemiology. J Mar Med Soc 2018;20:38-43

How to cite this URL:
Chatterjee K, Kunwar R, Taneja G, Mitra S, Srinivas V. An outbreak of varicella among troops on the move: A challenge in field epidemiology. J Mar Med Soc [serial online] 2018 [cited 2018 Dec 14];20:38-43. Available from: http://www.marinemedicalsociety.in/text.asp?2018/20/1/38/236244


  Introduction Top


Chicken Pox (Varicella) caused by Varicella zoster virus is one of the eight herpesviruses known to infect humans.[1] Historically, children 5–9 years old are commonly infected accounting for 50% of cases. It can cause a wide variety of symptoms ranging from maculopapular or vesicular rash in various stages of evolution, low-grade fever, and malaise to rash with hemorrhagic base and visceral complications, depending on the immune status of the patient.[2] The incubation period is usually between 14–16 days although with a range of 10–21 days.[3] Since the disease is communicable from 1-2 days before the rash till 4-5 days after and it has a very high secondary attack rate approaching 90% in household contacts, an outbreak in crowded areas or in barracks could assume serious proportions.[3]

Outbreaks of chicken pox get reported quite often in India since, as yet, routine vaccination against chicken pox has not been included in National Immunization Policy.[4] We report here an outbreak which occurred among military personnel who were part of turnover movement of an infantry battalion in the north-eastern part of the country. In the train carrying these personnel, two soldiers were in the incubation period of chicken pox. Thus, the other soldiers traveling in the train also acquired infection, and the disease, in the subsequent days, reached outbreak proportions requiring urgent containment measures. The investigation and control strategy adopted enabled us to learn a valuable lesson in field epidemiology.


  Methodology Top


Outbreak investigations conducted in field setup pose a challenge to the public health specialist since they begin without clear hypotheses but present with a pressing need to take action to stop the progress of disease and to take a deliberate decision as to when to consider that the data accumulated are sufficient to take action.[5]

Study setting

This cross-sectional study describes an outbreak of chicken pox among troops of an infantry battalion which moved from its old location to a new place. Cases started occurring while the troops were in the military special train. Soon after reaching its destination, the battalion underwent training at an Operational Training School and subsequently participated in operational area familiarization. Many contacts of the index cases, who traveled in the same train, developed chicken pox over subsequent days and were admitted and treated in the dependent hospitals. Contact tracing was carried out as per protocol developed; laboratory investigations were conducted; screening and precautionary measures were instituted.

Due to the rapid movement of troops after reaching their designated location, control measures were needed to be improvised and instituted to suit the operational requirements. Sensitization of the authorities in the battalion and formation headquarters enabled implementation of measures to control the outbreak. Regimental medical officer of the battalion and his medical team were co-opted to identify all probable cases at the earliest and segregate them. The susceptible population of affected subunits (companies) were segregated from rest of the battalion and kept under surveillance.

In the period between the battalion's return from training and moving out for familiarization of operational area, two companies at risk were held back to prevent mixing with other susceptibles. They were moved 2 weeks after rest of the battalion, to operational area. This was to identify, at the earliest, any case occurring up till the median incubation period of disease among population at risk. Operational commitment required that these troops participate in the familiarization and thus could not be held back any further.

Case definition and data collection

Probable cases were defined as those with acute onset of maculopapular or vesicular rash, with fever, who traveled in the military special train in which the main body of the battalion had moved. In the presence of only basic laboratory facilities in the hospital, confirmation of viral infection was not undertaken.

Background history of any troops admitted to military hospital at their previous location, till 1 month before movement of the battalion, was ascertained from unit records and military hospital authorities in the previous station. Epidemiological case sheet was developed for each case, and line lists were made. Laboratory investigations available in the hospital were undertaken for all cases. Chicken pox cases reporting to the hospital, not belonging to the battalion, or with no history of contact with other cases were excluded from the study. The outbreak lasted for approximately 2 months from the index cases.

Control measures adopted

All persons at risk were segregated in separate barracks. Contacts of new cases were subjected to detailed examination in the morning and evening till maximum incubation period of disease. Training activities for these personnel were halted. Their food was cooked from designated separate cookhouse, to minimize contact with susceptibles. Battalion personnel were sensitized by a continuous awareness campaign regarding the disease, to encourage self-reporting. Buddy pairs were tasked to assist in surveillance. Living barracks were ventilated, and cleaning activities in them were carried out. An effort was made to identify all personnel of the same companies who had a previous history of chicken pox and they were made to stay close to the contacts of any reported case, thereby forming a barrier of immunized persons around the contacts. Since the number of susceptibles in the two subunits was large, the option of vaccination was not resorted to.

All patients were managed with tablet acyclovir 800 mg five times a day and symptomatic therapy with emollients and anti-allergics. Surveillance was continued till last week of April 2016, covering maximum incubation period of disease.


  Results Top


Twenty-one cases of chicken pox occurred in the battalion within 3 months of their arrival at new location. Of these, two occurred in the military special train, six at the new location, eleven at the training school, and two during familiarization in operational area. All were admitted to dependent military hospitals and isolated. Fifteen cases belonged to Delta Company, three were from Support Company, two from Military Transport Platoon, and one from Bravo Company [Figure 1]. Of these, the last case was reported on April 23, 2016 but had no history of contact with the previous cases and had arrived back after a long military course. Thus, a total of only twenty cases were included in the study. Distribution of cases is as shown in [Table 1].
Figure 1: Distribution of cases as per companies (subunits)

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Table 1: Description of occurrence and distribution of cases

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First two cases belonging to Delta Company were detected on January 15, 2016 on the military special train and were referred to the dependent hospital at their destination, isolated and managed as chicken pox cases by the physician. The battalion, instead of proceeding to its new location, left for operational training school, from its destination railway station. In this school, eleven cases occurred during the course of training and were admitted and treated in the dependent hospital. The susceptible troops of affected companies were segregated by local authorities and did not participate in any training till the battalion moved back to its designated new location by February 17, 2016.

Before moving out for their operational commitments again on February 22, 2016, three more cases were detected. To halt further spread of disease, the personnel at risk belonging to Delta and Support Companies were held back and not allowed to proceed with rest of the battalion for operational area familiarization till February 29, 2016. No case was reported among these two companies till then. In the operational area, two more cases occurred, who were admitted and isolated at the nearest hospital. The battalion arrived back at new location by 1st week of March 2016, and subsequently, three more cases were detected.

The index cases gave history of admission in military hospital for review of other morbidities, at their previous station, and were discharged on January 01, 2016. The same day they travelled with the battalion to a neighboring city where they stayed till boarding the military special train on January 10, 2016. Both these cities had reports of chicken pox cases occurring among local military population. However, a clear contact history could not be elicited for these cases. Contact tracing of all cases occurring after them revealed exposure to at least one person who subsequently developed the disease in the battalion. An epidemic curve for time distribution of cases was prepared [Figure 2], which showed that ten cases occurred within the incubation period of index cases, who later managed to propagate the disease among rest of the troops. The secondary attack rate for this disease was calculated to be 24%. Three cases were Non Commissioned Officers (NCOs) and seventeen were Sepoys. All were below thirty-five years of age.
Figure 2: Epidemic curve: index cases reported on January 15 and peak of outbreak occurred on February 3. Active intervention carried out from February 17 onward

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All cases presented with fever, maculopapular or vesicular rash, pleiomorphic in nature, body ache and itching all over the body. None gave a positive history of chicken pox in childhood. There was no available record for any vaccination against the disease for the cases. All reported to hospital immediately on occurrence of rash. There was no overcrowding observed in the unit barracks. Among the seven cases admitted to this hospital, all underwent routine blood hemogram, biochemistry, and routine urine examination without any significant findings. None of the cases developed any complications and recovered completely from the disease as is depicted in [Table 2].
Table 2: Demographic and clinical profile of the cases

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During the period of observation up till end of April 2016, there were five cases of chicken pox among other units in this station but who had no contact with any personnel under study.

Epidemiological linkage between the cases was studied and has been depicted in [Figure 3].
Figure 3: Epidemiological Linkage between the cases of Chicken Pox admitted to different hospitals

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  Discussion Top


The present outbreak occurred among troops, residing in barracks or traveling together, highlighting the vulnerability of military populations and has been reported among troops in various studies.[6] This vulnerability increases when the troops engage in military exercises, where arrangements for accommodation are ad hoc and highly communicable diseases easily spread. Constant movement of affected subunits resulted in further spread of the disease in the present instance. Since chicken pox is known to be communicable from 2 days before rash appears, it caused an explosive spread among troops, given the circumstances, and presented a challenge for observing precautionary measures.

The months from January to March have extreme cold weather conditions in North East of India. This might have resulted in huddling together of susceptibles, wherever they stayed. This setting in winters is perfect for spread of the disease, with community which is naïve to the disease or nonimmune, living in proximity, which leads to rapid transmission of the virus.[7]

The epidemic curve [Figure 2] shows that the index cases were able to spread the infection to susceptible population of the battalion traveling with them in military special train. Some of the latter became symptomatic while undergoing training in training school and caused a peak in incidence of cases.

At the new location, the troops were subjected to intense control, prevention, and surveillance measures, and only four cases reported thereafter. Of these, three occurred within the incubation period after exposure to the last case on February 19, while the fourth reported to the hospital on March 24, after institution of preventive measures. This gave an indication that aggressive preventive measures played a significant role to control the outbreak.

Most personnel, having been sensitized to the need for early reporting, came to medical attention immediately on development of constitutional symptoms and thus were identified at the initial stage of period of communicability. the secondary attack rates of disease in the present study were low compared to that mentioned in standard texts of 60%–100%.[8] This could be due to the impact of early control measures and segregation instituted during train journey.

The study highlights the importance of taking into confidence the executive authorities and eliciting their support in instituting preventive measures. As per the Defence Service Regulations, health of troops is the primary responsibility of Commanding Officers of the battalion.[9] Informing them of the measures taken, explaining the objectives and requirements of any investigation, and establishing a close rapport help in obtaining a lot of information with less resistance and garnering their support.[10]

The authors could not rule out the possibility of childhood occurrence of chicken pox, which might have led to presence of immunity among the contacts of cases. This could not be proved due to lack of laboratory confirmation of antibody titer and is a limitation of the study.

There was no history of vaccination among the troops in the study. Vaccination is an effective strategy in preventing chicken pox.[11] The disease may have more severe presentation with likelihood of complications among adults; however, in our study, there were no complications reported among the affected population. Although breakthrough varicella has been reported after vaccination, it is substantially less severe with less median number of lesions and it is of shorter duration and with lower incidence of fever as compared to unvaccinated persons.[6],[12] Hence, it is important that awareness regarding the vaccination is highlighted among military personnel.

This outbreak served to provide few important lessons in the practice of epidemiology in the field.

  1. Awareness about the potential of index cases, such as occurred in the beginning of this study, to obtain outbreak potential and take aggressive prevention measures to prevent propagation of the disease
  2. Heightened sense of urgency in situ ations such as outbreaks can raise its emotional impact on all involved persons and groups.[5] Advice on preventive measures therefore needs to be provided at the earliest and tailored to best available alternative in view of operational commitments. Various steps to limit breakdown of segregation and other preventive measures in the background of rapid and continuous movement of the affected troops were highlighted in this study
  3. Data were sourced from unit records of three hospitals to arrive at the probable chain of transmission of disease and institute control measures alongside conduct of investigation of how the disease was being spread
  4. Commanders and executive officers were brought into confidence and the impact of a highly communicable disease like chicken pox, on training and operational commitments, was explained to them
  5. The study also points out to the importance of raising the immune status of young adult military population by vaccination strategy. This has already been brought out as an advisory for Armed Forces. The Armed Forces are a special group of persons who work in a distinct scenario; hence, its successful implementation needs to be ensured among the personnel.



  Conclusion Top


Chicken pox has been known to cause outbreaks in barracks, institutions, and schools. In adults, it may result in severe disease. In the present study, chicken pox had the potential to pose a bigger threat due to close congregation of troops, favoring ease of spread. Aggressive intervention measures, combined with surveillance efforts and awareness program, resulted in halting this situation. In the absence of vaccination, the institution of other preventive measures such as segregation and early identification was successful. The lessons learnt could be utilized in other such instances of field investigation of outbreaks.

Recommendations

Chicken pox vaccination, which has proven efficacy, should be aggressively pursued to be implemented in Armed Forces. The efficacy of a well-established surveillance or health intelligence system has been proven time and again and is an inescapable need in all health-care settings.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Cook GC, Zumla A, editors. Cutaneous viral diseases. In: Manson's Tropical Diseases. 21st ed. London: ELST with Saunders; 2003. p. 848-54.  Back to cited text no. 1
    
2.
Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, editors. Varicella-Zoster virus infections, Harrison's online. Harrison's Principles of Internal Medicine. 18th ed., Ch. 180. New York: Access Medicine from McGraw Hill; 2011.  Back to cited text no. 2
    
3.
Park K. Park's Textbook of Preventive and Social Medicine. 23rd ed. Jabalpur: M/s Banarsidas Bhanot; 2015. p. 143-6.  Back to cited text no. 3
    
4.
Bhatti VK, Budhathoki L, Kumar M, Singh G, Nath A, Nair GV, et al. Use of immunization as strategy for outbreak control of varicella zoster in an institutional setting. Med J Armed Forces India 2014;70:220-4.  Back to cited text no. 4
    
5.
Goodman R, Buehler JW. Field epidemiology defined. In: Gregg M, editor. Field Epidemiology. 3rd ed. New York: Oxford University Press; 2008. p. 3-15.  Back to cited text no. 5
    
6.
Goh JJ, Ho M, Koh WM, Lee VJ. An economic analysis of varicella immunization in the Singapore military. Mil Med Res 2016;3:3.  Back to cited text no. 6
    
7.
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.  Back to cited text no. 7
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8.
Jumaan A, Lavanchy D. Chickenpox/herpes zoster. In: Heymann DL, editor. Control of Communicable Diseases Manual. 19th ed. Washington: APHA; 2008. p. 109-16.  Back to cited text no. 8
    
9.
Defence Services Regulations, Regulations for the Army. Delhi: The Controller of Publications; Revised – 1987.1.p 13.  Back to cited text no. 9
    
10.
Bhalwar R. Investigation of an epidemic. In: Public Health and Preventive Medicine for the Indian Armed Forces. The “Red Book”. 8th ed. Pune, New Delhi: Director General Armed Forces Medical Services, Ministry of Defence; Reprinted-2011. p. 40-51.  Back to cited text no. 10
    
11.
Weekly Epidemiological Record: WHO Position Paper on Varicella Vaccines. Vol. 73. World Health Organisation; 1998. p. 241-8.  Back to cited text no. 11
    
12.
Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. Hamborsky J, Kroger A, Wolfe S, eds. 13th ed. Washington D.C. Public Health Foundation, 2015. p.353-76. Available from: http://www.cdc.gov/chickenpox/references.html. [ Last accessed on 2016 Jun 19].  Back to cited text no. 12
    


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