Abstract
Background
On the 2nd and 3rd December 2023, a cluster of nine acute febrile illnesses with parotidomegaly was reported among students of a kindergarten in a South-West coastal district of India. We investigated the outbreak to identify the illness, to describe the outbreak in terms of time, place and person, to identify the factors responsible for the spread, and to control the disease.
Methods
The investigation was conducted in a military setting at a South-West coastal district of India from December 2023 to January 2024. Clinical and epidemiological data of the initial cases were captured using a data abstraction sheet from healthcare establishments, kindergartens and schools to make operational case definitions. We did an active house to house surveillance to detect additional cases till 26 January 2024, i.e. for six weeks after the last case was detected. The descriptive analysis was done by calculating the incidence as per age, gender and vaccination status, plotting of an epidemic curve and preparation of spot maps to understand the spread of cases. We also conducted a matched case–control study to test the hypothesis that clustering of unvaccinated kindergarten students was the cause of this Mumps outbreak.
Results
The index case was identified as Mumps on 02 December 2023 in the Paediatric department of the hospital. A total of 52 cases of Mumps occurred with an attack rate of 1.8%. Forty-five out of the 52 affected children were from Kindergarten and the rest from primary and middle school. The outbreak started on 02 November 2023, peaked on 04 December 2023 and ended on 15 December 2023 after rapid institution of control measures. The incidence was highest (5.5%) in children aged four and five years. There was clustering of cases in kindergarten. Nearly 60% of the cases were unvaccinated against Mumps. Vaccination against Mumps was found to be protective against Mumps.
Conclusion
This outbreak of Mumps was probably due to close interaction of unvaccinated children in the kindergarten. Students contracting Mumps lose classes and the disease is known to cause complications when occurring later in life. Hence, we recommend Mumps vaccination during childhood to prevent such outbreaks.
Keywords: Mumps, Vaccination, Healthcare, Pre-school, Kindergarten
Introduction
Mumps is generally seen in children of school going age and presents as an acute febrile illness with parotidomegaly or swelling of other salivary gland(s).1 One in every five Mumps infections is asymptomatic. The infection is transmitted via respiratory droplets and fomites which makes it highly contagious. The secondary attack rate is extremely high ranging between 65% and 87%.2,3 The disease is generally self-limiting and resolves within ten days. The complications though rare are severe, namely encephalitis, meningitis, deafness, orchitis, and oophoritis. There has been a significant decline in Mumps since the introduction of the vaccine in 1967.
About 80% of children are not given Mumps vaccination due to noninclusion of the same in the Universal Immunisation Program in India.4 Hence, the birth cohorts in pre-school or kindergarten are largely unvaccinated against Mumps. Due to waning immunity, older children who had received their last dose more than 10 years ago are also at risk.3 Reports from the Integrated Disease Surveillance Programme have suggested an increase in Mumps outbreaks over the past two years in both young and older children.5 Studies confirm that even in a fully vaccinated population, some individuals may get infected. But they are at a much lower risk for developing the disease and its complications.6 Due to these factors, Mumps has a huge potential to cause outbreaks in closely interacting communities like schools, prisons, etc.
On the 2nd and 3rd December 2023, a cluster of nine acute febrile illnesses with parotidomegaly was reported among students of a kindergarten in a South-West coastal district of India. We conducted an epidemiological study to identify the illness, to describe the cases in terms of time, place and person characteristics, to identify the factors responsible for the spread, and to recommend measures to control the disease.
Materials and methods
Descriptive study
The study was conducted in a large military setting at a South-West coastal district of India in December 2023 and January 2024. We captured clinical and epidemiological data of the initial cases using a data abstraction sheet from review of outpatient and inpatient records of healthcare establishments and dispensary records of the kindergarten and schools. Based on the analysis of these initial cases and World Health Organization (WHO) reference case definition, a case definition for this study was formed. We defined a suspect case as a child or adolescent residing in a military setting in a South-West coastal district who had acute onset of unilateral or bilateral tender swelling of the parotid or other salivary gland and without other apparent cause, with or without fever in December 2023 and January 2024.7 We defined a probable case as a suspect case who had any contact with a suspect case. Laboratory tests to isolate Mumps virus were not carried out.
We used the case definitions for active case detection in the kindergartens, schools and door-to-door search in the military setting using an interview-based questionnaire. The active case detection was done till 26 January 2024, i.e. for six weeks after the last case was detected (the longest incubation period of Mumps being three weeks). The information gathered through questionnaire included date of onset of symptoms, sequence of appearance and duration of symptoms, contact with similar case, travel history, past history of Mumps, certain relevant demographic details and vaccination status for Mumps as per vaccination card record. The data were collected from parents of children (younger than 12 years) during house visits, children (older than 12 years) at schools, and teachers of the kindergartens and schools.
The data were entered in Microsoft Excel 2019 and analysed using Epi-Info version 7.2.1.0 (CDC, Atlanta, USA). From the line-list of cases, a descriptive analysis of the outbreak was done. The incidence was calculated using population denominators. An epidemic curve was plotted for time trend. A spot map was drawn as per place of residence and school to understand the spread of cases. Person analysis was done as per age, gender and vaccination status. Categorical data were summarised using proportions; continuous data were summarised using means and standard deviations. Epidemiological links were prepared through history and social links to find the probable source of infection.
Matched case–control study
We conducted a matched case–control study to test the hypothesis that clustering of unvaccinated kindergarten students was the cause of this Mumps outbreak. All children of kindergarten with Mumps as per the line-list were considered as case patients. For each case patient, we recruited one age and gender-matched control attending the same class and section of the kindergarten. The vaccination status against Mumps from the vaccination card was collected from the cases and controls.
Matched odds ratio (mOR) for discordant pairs and their 95% confidence intervals (CIs) along with population preventive fraction was calculated using Epi-Info version 7.2.1.0 (CDC, Atlanta, USA).
Institutional Ethics Committee approval was taken for the study. All the guidelines as per declaration of Helsinki and good clinical care practice guidelines as per WHO was followed while taking consent from the parents/guardians of the patients prior to data collection and the purpose and nature of investigation was explained. Concurrently, necessary health advice for prevention of Mumps was provided to parents, teachers and children and control measures were instituted.
Results
The military setting in a South West Coastal district has a kindergarten and two schools. Most of the students of these educational institutes reside in the military setting. In the military setting, healthcare is provided by a primary care clinic which is located in the residential area and a hospital with a paediatrician.
On the 2nd and 3rd December 2023, a cluster of nine acute febrile illnesses with swelling of the cheek near the ear was reported among students of a kindergarten in a South-West coastal district of India. The index case was identified as Mumps in the paediatric department of the hospital. During the initial investigation, we found similar cases in the kindergartens and schools within the military setting.
Concurrent to the outbreak investigation, control measures against Mumps were instituted and health advisories were widely disseminated. Parents were advised not to send their child to the kindergarten and schools if they had the symptoms of flu-like illness and/or swelling of parotids. Furthermore, schools were requested to postpone any cultural and sports activities. In addition, active case detection was started to isolate the cases at home. The contacts of the cases were also quarantined at home. All cases were examined and provided symptomatic treatment. They were followed up for early detection of complications; however, none of them reported any.
Descriptive study
We identified a total of 52 case patients with an attack rate of 1.77 %. The cases occurred in an age group of four to seventeen years with the highest attack rate (5.54%) in the children attending kindergarten (four and five years). Attack rates were similar in both genders (Table 1). Nearly 60% of the cases were unvaccinated against Mumps. Age-wise proportion of unvaccinated children among Mumps cases ranged from 52% to 100% and did not have any specific pattern (Chi-Square p > 0.05) (Table 2).
Table 1.
Age and gender specific attack rates (N = 2935).
| Characteristics | Cases | Population in military setting | Attack rate (in percentage) | |
|---|---|---|---|---|
| Age (in years) | 4 | 12 | 284 | 4.22 |
| 5 | 27 | 420 | 6.42 | |
| 6 | 6 | 300 | 2.00 | |
| 7 | 1 | 264 | 0.40 | |
| 8 | 3 | 247 | 1.21 | |
| 9–17 | 3 | 1420 | 0.21 | |
| Gender | Male | 30 | 1596 | 1.88 |
| Female | 22 | 1339 | 1.64 | |
| Overall attack rate | 52 | 2935 | 1.77 | |
Table 2.
Age-wise proportion of unvaccinated children among Mumps cases (N = 52).
| Age (in years) | Cases unvaccinated against Mumps | Mumps cases as per age group | Proportion of unvaccinated children among Mumps cases as per age groups |
|---|---|---|---|
| 4 | 7 | 12 | 58.3 % |
| 5 | 14 | 27 | 51.9 % |
| 6 | 6 | 6 | 100 % |
| 7 | 0 | 1 | – |
| 8 | 2 | 3 | 66.3 % |
| 09–17 | 2 | 3 | 66.3 % |
| Total | 31 | 52 | 59.6 % |
All cases had either bilateral or unilateral parotid gland swelling. The majority had fever (92.3%) followed by ear pain (96.2%), running nose (82.7%) and difficulty in swallowing (78.8%) (Table 3).
Table 3.
Distribution of symptoms among Mumps cases (N = 52).
| Symptom | Number of cases | Percentage |
|---|---|---|
| Salivary gland swelling | ||
| Bilateral parotidomegaly | 32 | 61.5 |
| Unilateral parotidomegaly | 12 | 23.0 |
| Submandibular | 7 | 13.5 |
| Fever | 48 | 92.3 |
| Ear pain | 50 | 96.2 |
| Running nose | 43 | 82.7 |
| Difficulty in swallowing | 41 | 78.8 |
| Cough | 24 | 46.1 |
Clustering of cases was observed in kindergarten and not as per the residence, which was probably the place where the infection spread (Fig. 1, Fig. 2).
Fig. 1.
Schematic spot map (not as per scale) of Mumps cases in residential areas at a military setting, South Western coastal state of India (N = 52).
Fig. 2.
Spot map of Mumps cases in kindergarten at a military setting, South Western coastal state of India (N = 39).
The primary case occurred on 02 November 2023. The index case occurred on 02 December 2023. The kindergarten and schools had reopened in the third week of November 2023, after 14 days of vacation. The outbreak peaked on third–fourth December 2023 and with rapid institution of control measures receded by the 2nd week of December 2023. The last case occurred on 15 December 2023 (Fig. 3).
Fig. 3.
Mumps cases in kindergarten and schools in a military setting, November–December 2023, as per date of onset of symptoms (N = 52).
We also found that the incidence of cases was higher in parents with inadequate knowledge about Mumps (55.8% vs 44.2%, Chi-Square p 0.02) as they allowed children with mild symptoms to attend sports and cultural activities in the first week of December 2023.
Case control study
Based on the findings of the descriptive study, we hypothesised that clustering of unvaccinated kindergarten students was the cause of this Mumps outbreak. The investigation team recruited all the 39 case patients attending kindergarten and their matched controls in a 1:1 ratio. The case–control pairs were analysed as per the vaccination status against Mumps. The odds of vaccination among Mumps cases were 0.22 times the odds of vaccination among controls (conditional maximum likelihood estimate (CMLE) of odds ratio (OR): 0.22, 95% CI: 0.06, 0.62; Table 4). Population preventable fraction (PPF) was 80.7 % (95% CI: 68.4, 93.1).
Table 4.
Case–control pairs according to vaccination status in a military setting, December 2023.
| Number of case–control pairsa | Controls |
Total | ||
|---|---|---|---|---|
| Unvaccinated | Vaccinated | |||
| Mumps cases | Unvaccinated | 5 | 18 | 23 |
| Vaccinated | 4 | 12 | 16 | |
| Total | 9 | 30 | 39 | |
CMLE odds ratio (95% CI): 0.22 (0.06–0.62).
Population preventive fraction (95% CI): 80.7% (68.4–93.1%).
CMLE OR: Conditional maximum likelihood estimate of odds ratio; CI: confidence interval.
39 case–control pairs with 22 discordant pairs.
Discussion
There was a sudden surge in cases of acute febrile illness with parotidomegaly, post reopening of kindergarten among pre-school children aged four to six years in the first week of December 2023. The index case was a four-year-old child who reported to the paediatric department of hospital. The cases were also reported by the primary care clinic which prompted an epidemiological investigation by the authors. Fifty-two cases of Mumps occurred during the study period with an attack rate of 1.77 %. The highest attack rate (5.54%) was in the pre-school children (four and five years). The cases were mostly clustered in the kindergarten.
Sporadic outbreak of Mumps cases were reported from various parts of India in the same period.8 Further, multiple laboratories confirmed that Mumps outbreaks were reported in various districts of Kerala such as Palakkad, Alappuzha, Idukki and Thiruvananthapuram among four- to twelve-year-old children in November and December 2023.5 Hence, there was probably a risk of importing the infection while visiting native places during vacations in last week of November 2023.
Several studies have reported low efficacy of Mumps component of the measles, mumps, and rubella (MMR).9,10 Further, some studies have shown that Mumps can also infect persons who have suboptimal seroconversion (primary vaccine failure) or those with waning immunity after 10 years of primary vaccination (secondary vaccine failure).11,12 Due to these reasons, Mumps vaccine was discontinued from the National Immunisation Program in India since 2019. Currently, the birth cohorts of last six years are largely unvaccinated against Mumps and frequent outbreaks are being reported in this age group, like in our study.
Studies have showed surge in Mumps cases in settings such as schools, dormitories and slums when the vaccination coverage decreases.11,13, 14, 15 Insufficient seroprevalence of Mumps antibodies has been shown in a large study among school children in India in 2015.15 In order to achieve herd immunity and prevent Mumps outbreak, an immunisation coverage of more than 90% is required.
In our study, nearly 60% of Mumps cases were unvaccinated against Mumps. This may have resulted in increase in the secondary attack rate among classroom contacts; thereby facilitating the transmission of Mumps virus. In this outbreak, vaccination against Mumps protected kindergarten students against Mumps infection (CMLE OR: 0.22, 95% CI: 0.06, 0.62) and nearly 81% cases were avoided due to the Mumps vaccination (PPF: 80.7 %, 95% CI: 68.4, 93.1). Mumps vaccination is still being continued in several developed countries as part of their national immunisation programme. Mumps-related morbidities including encephalitis and deafness have declined significantly in counties with high coverage of mumps vaccine.16 Hence, we recommend Mumps vaccine during childhood with a booster dose for maintaining optimum seroprevalence of antibodies against Mumps and to prevent outbreaks. Our recommendation is in line with the Armed Forces immunisation program, in which Mumps containing vaccine in the form of MMR vaccine has been introduced for children.
We could not carry out confirmatory laboratory tests due to limitation in laboratory facility. However, outbreaks of Mumps occurred in adjoining districts in Kerala during the same period and were confirmed with laboratory tests.
Conclusion
An outbreak of Mumps was reported in a military setting in a South-West coastal district of India mainly affecting pre-school children (39 out of the 52 cases) attending a kindergarten. The outbreak was probably due to close interaction of children in the kindergarten, most of whom were unvaccinated against Mumps (mOR: 0.22, 95% CI: 0.06, 0.62). Students contracting Mumps lose classes and the disease is known to cause complications when occurring later in life. Hence, we recommend Mumps vaccine during childhood for maintaining optimum seroprevalence to prevent outbreaks.
Patients/ Guardians/ Participants consent
Guardians/parents informed consent was obtained.
Ethical clearance
Institute/hospital ethical clearance certificate was obtained.
Source of support
None.
Disclosure of competing interest
The authors have none to declare.
Acknowledgements
None.
References
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