Resurgence of mumps in Gujarat: Diagnostic insights, breakthrough infections, and immunization gaps

INTRODUCTION

Mumps is an acute viral infection caused by the mumps virus, a single-stranded RNA virus belonging to the Paramyxoviridae family. While only one serotype of the virus exists, it has been classified into 13 genotypes based on the sequence of the small hydrophobic (SH) protein.^[1] Transmission occurs primarily through respiratory droplets, and the disease typically manifests with nonspecific symptoms such as fever, malaise, and headache, followed by the hallmark swelling of the parotid and other salivary glands.

Although mumps is often a mild disease, especially in children, complications can occur, and these are notably more common and severe in adults. Major complications include epididymo-orchitis, oophoritis, aseptic meningitis, encephalitis, and pancreatitis.^[2]

Prevention through vaccination is the cornerstone for controlling mumps outbreaks. The mumps vaccine consists of live attenuated strains such as Jeryl-Lynn RIT 4385, Leningrad-3, Leningrad-Zagreb, Rubini, and others. In India, most vaccine manufacturers rely on the Leningrad-Zagreb strain.^[1] However, the National Immunization Program of India does not currently include the mumps vaccine as a part of routine immunization. In contrast, the Indian Academy of Pediatrics (IAP) recommends two doses of the measles, mumps, and rubella (MMR) vaccine – administered at 9 months and 15 months of age.^[3,4]

Recently, an alarming surge in mumps cases has been observed across multiple Indian states, including Gujarat, Maharashtra, Uttar Pradesh, Odisha, and Rajasthan, particularly during 2023–2024. This resurgence, following a gap of 4–5 years, raises concerns about waning immunity, missed vaccination opportunities, and evolving virus epidemiology. Factors such as suboptimal vaccine coverage, inadequate booster doses, and changes in the virus dynamics may contribute to this rise.

In this context, our hospital-based study was conducted at a tertiary care center in western Gujarat to investigate the occurrence of breakthrough mumps cases, defined as mumps infection occurring despite prior vaccination. We specifically asked: Among clinically diagnosed mumps patients, what is the relative diagnostic yield of reverse transcription polymerase chain reaction (RT-PCR) (buccal swab and urine) versus immunoglobulin M enzyme-linked immunosorbent assay (IgM ELISA) across illness days, and what is the proportion of breakthrough infections in a lowMMR-coverage setting? Although clinical diagnosis remains primary, laboratory confirmation is critical for surveillance, outbreak control, and distinguishing breakthrough infections where clinical presentation may be atypical. The study also aimed to bridge the existing diagnostic gap by confirming cases through molecular and serological testing. Such studies are crucial for understanding local disease dynamics, evaluating the effectiveness of vaccination programs, and identifying potential gaps in immunity. In addition, the findings can provide valuable insights to guide public health interventions, strengthen vaccination strategies, and help prevent future outbreaks of mumps in the region.

MATERIALS AND METHODS

This prospective, cross-sectional, hospital-based study was conducted at the All India Institute of Medical Sciences (AIIMS), Rajkot, Gujarat, over a 6-month period from March 2024 to September 2024. The study included both pediatric and adult patients presenting with clinical features suggestive of mumps, such as fever, parotid gland swelling, and associated symptoms. Patients (or their parents/guardians in the case of children) who provided written informed consent were included, while those unwilling to provide consent were excluded.

Relevant clinical information, including demographic details, presenting symptoms, vaccination history, and complications (if any), was collected using a standardized case record form. To ensure a comprehensive diagnostic evaluation, three types of samples were collected from each patient, irrespective of the stage of illness. A blood sample was obtained to detect mumps-specific IgM antibodies using an IgM ELISA employing the NOVATEC Germany Mumps Virus IgM Antibody ELISA kit (Cat No. MUMM0340; Lot No. MUMM-138N/MUMM-133; expiry September 30, 2025/January 31, 2025) according to the manufacturer’s instructions. Buccal swabs (collected from the parotid duct area) and urine samples were obtained for viral RNA detection by RT-PCR, targeting the SH gene, following the protocol of Vaidya et al. 2013.^[5]

All collected samples were stored and transported under appropriate cold chain conditions to the National Institute of Virology, Pune, for confirmatory testing. The rationale for testing multiple sample types stemmed from the variable shedding of the mumps virus in different biological fluids. Buccal swabs and urine samples were tested using RT-PCR to maximize the detection of viral RNA, particularly in the early stages of infection. Simultaneously, IgM antibody testing through ELISA ensured the identification of cases in the later stages of illness, thereby providing a robust diagnostic framework for mumps confirmation. This approach minimized diagnostic gaps and enhanced the reliability of case detection.

This study was conducted after obtaining approval from the Institutional Ethics Committee (IEC), AIIMS Rajkot, with approval number AIIMS/RAJKOT/5TH IEC/FB/35.

RESULTS

A total of 48 suspected cases of mumps were reported during the study period. Among these, 31 (64.58%) were male, and 17 (35.42%) were female patients. Notably, none of the patients presented with recognized complications (encephalitis, meningitis, orchitis, or pancreatitis); our cohort thus comprised largely uncomplicated cases. Nonetheless, molecular diagnostics yielded high sensitivity across sample types. Age distribution revealed that 31 (64.58%) were children (≤15 years), and 17 (35.42%) were adults [Table 1].

Out of the 48 suspected cases, 43 (89.58%) were confirmed for mumps using one or more diagnostic tests, while 5 cases (10.42%) tested negative for all tests. Anti-mumps IgM was detected in 70.8% (34/48) of patients; 14.6% (7/48) were negative, and 14.6% (7/48) equivocal. Notably, all seven equivocal samples for IgM ELISA tested negative for viral RNA by RT-PCR of throat swabs, highlighting the superiority of RT-PCR for diagnosing mumps, particularly in the 1^st week of illness when serology may yield inconclusive results [Figure 1].

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Figure 1:

Test-wise confirmed cases amongst the children and adults. IgM: Immunoglobulin M; RT-PCR: Reverse transcription polymerase chain reaction.

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For molecular detection, RT-PCR on buccal swabs demonstrated higher sensitivity with 34 cases (70.83%) testing positive compared to 10 cases (20.83%) detected from urine samples [Figure 2]. Of the 34 patients positive by buccal-swab RT-PCR, 23 (67.6%) were detected within the first 3 days of illness and 11 (32.4%) thereafter; by contrast, of the 34 patients positive by IgM ELISA, 21 (61.8%) seroconverted within days 1–3 and 13 (38.2%) after day 3 – reflecting the shift from early viral shedding to later antibody response. This emphasizes that buccal swabs are a more reliable sample type for detecting viral RNA in the acute phase of mumps infection.

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Figure 2:

Number of cases according to days of illness. IgM ELISA: Immunoglobulin M enzyme-linked immunosorbent assay, RTPCR: Reverse transcription polymerase chain reaction.

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Of particular interest, two breakthrough mumps cases were identified among vaccinated individuals, indicating the possibility of waning immunity or vaccine failure. However, a significant challenge in identifying breakthrough infections was the lack of vaccination recall, as 17 patients (35.42%) were unaware of their vaccination status. We verified records where available; otherwise, we acknowledge potential recall bias in self-reported vaccination history. Among the remaining patients, 29 (60.42%) reported no prior vaccination, underlining the need for improved immunization coverage and awareness [Table 1].

Statistical analysis revealed significant associations between age, vaccination status, and diagnostic outcomes. A Chi-square test demonstrated a significant association between age group (≤15 years vs. >15 years) and RT-PCR positivity on buccal swabs (χ² = 32.17, P < 0.001), with children being significantly more likely to test positive. In addition, Cohen’s Kappa statistic showed a perfect agreement between IgM ELISA positivity and RT-PCR positivity for buccal swabs (Kappa = 1.0), suggesting excellent diagnostic consistency. A Fisher’s exact test further revealed a significant association between vaccination status and RT-PCR positivity (P < 0.001), where unvaccinated individuals were significantly more likely to test positive for mumps compared to vaccinated individuals.

These findings underscore the importance of molecular diagnostic methods like RT-PCR for the early and accurate diagnosis of mumps, particularly in the acute phase of illness or when serological results are inconclusive. The study also highlights critical gaps in immunization coverage and vaccination recall, emphasizing the need for strengthened vaccination programs and public health initiatives to reduce the burden of mumps.

DISCUSSION

Mumps remains a significant public health issue, particularly in regions with low vaccination coverage. Although mumps is primarily a clinical diagnosis, laboratory confirmation is essential for surveillance, outbreak control, and identifying atypical or breakthrough cases. According to the Global Health Observatory data, India reported 764 cases of mumps from 2021-2022, highlighting the substantial disease burden, particularly among children.^[6] The situation has worsened in 2023-2024, with rising cases reported across multiple Indian states, including Maharashtra, Uttar Pradesh, Odisha, Rajasthan, Kerala, Tamil Nadu, Chhattisgarh, and Gujarat. This study observed a similar trend, with 64.58% of cases occurring in children (≤15 years), reinforcing the vulnerability of younger populations during mumps outbreaks.^[7-9]

One significant factor contributing to these outbreaks is the non-inclusion of the mumps vaccine in the Universal Immunization Program (UIP) in India. UIP, which offers free vaccines to children, currently includes the Measles and Rubella (MR) vaccine but not the MMR vaccine. In contrast, the IAP recommends three doses of MMR at 9 months, 15 months, and 4-6 years of age.^[4] With nearly 80% of India’s population relying on government health services, the absence of mumps vaccination in UIP leaves a large proportion of children unprotected, making them susceptible to outbreaks.^[10] Studies have demonstrated the immunogenicity and effectiveness of the MMR vaccine, with long-term seropositivity for mumps antibodies up to 6 years post-vaccination.^[11,12] Introducing the third dose of MMR in outbreak settings has proven effective in regions such as the USA and Europe, where waning immunity has been a concern.^[13,14]

In this study, two breakthrough cases of mumps were observed, reflecting a growing concern worldwide. One case involved a 3-year-old vaccinated child, which might indicate primary vaccine failure, where an appropriate immune response fails to develop after vaccination. The second case, a 26-year-old fully vaccinated male, aligns with documented global trends of waning immunity over time, particularly in vaccinated adults. Studies from the USA and Europe have shown a rise in mumps infections among previously vaccinated populations, especially those vaccinated more than 10-15 years ago.^[15] These findings emphasize the need for booster doses in older age groups to maintain protective immunity.

The findings of this study highlight the importance of using molecular diagnostics, specifically RT-PCR, in diagnosing mumps. While PCR positivity in buccal swabs is highest during the early stages of illness, we quantified its relative yield against urine and IgM ELISA in our setting, thereby informing diagnostic algorithms for Indian tertiary centers. While IgM ELISA remains a valuable diagnostic tool, it has limitations, particularly in vaccinated individuals and early stages of infection. In our study, all seven equivocal IgM ELISA samples tested negative by RT-PCR, underscoring the superiority of RT-PCR in confirming mumps cases. RTPCR on buccal swabs demonstrated a significantly higher sensitivity (70.83%) compared to urine samples (20.83%), consistent with global research findings. This aligns with evidence that viral RNA is shed more consistently in buccal secretions during the early phase of illness.^[16] A small subset (5/48; 10.4%) of cases tested negative by both RT-PCR and IgM ELISA. This group may not represent true mumps but rather mumps-like parotitis caused by other pathogens (e.g., parainfluenza viruses, Epstein-Barr virus, influenza virus, adenovirus, or bacterial agents). Alternatively, these double negatives could reflect suboptimal specimen timing or quality. Hence, clinicians should interpret negative laboratory results in the context of clinical findings and consider alternative diagnoses or repeat testing where appropriate.

Moreover, with the widespread availability of RT-PCR infrastructure following the COVID-19 pandemic, molecular testing for mumps has become more accessible across India. Collecting and processing buccal swabs for RT-PCR is convenient, reliable, and facilitates early diagnosis, thereby enabling timely clinical management and outbreak control. It is important to note that serological tests among vaccinated individuals should be interpreted cautiously, as previous immunity may interfere with IgM responses. In such cases, RT-PCR serves as the preferred diagnostic method for confirming active infections. Per the Centers for Disease Control and Prevention/World Health Organization (WHO) recommendations, RT-PCR from buccal/oral swabs collected ≤3 The days of parotitis onset are considered the preferred confirmatory test; serology supports later-stage diagnosis.^[17]

The findings also highlight critical gaps in vaccination recall and coverage. In our study, 17 patients (35.42%) were unaware of their vaccination status, complicating the identification of breakthrough cases. In addition, 60.42% of patients reported no vaccination history, emphasizing the urgent need for improved public awareness and immunization coverage. Introducing the MMR vaccine into UIP could serve as a major preventive strategy, reducing mumps-related morbidity and addressing this immunization gap. Both WHO and IAP have advocated for including MMR in routine immunization programs, which has been successful in reducing mumps incidence globally.

The strength of this study lies in its comprehensive use of both molecular and serological methods to confirm mumps cases, providing robust diagnostic insights. The findings are particularly relevant for outbreak management and immunization policy improvements. However, the study is limited by its single-center design and relatively small sample size, which may not fully represent the epidemiology of mumps in other regions. In addition, reliance on patient-reported vaccination status introduces the risk of recall bias, particularly among adults.

CONCLUSIONS

This study highlights the resurgence of mumps in western Gujarat, predominantly among unvaccinated children and adults. The findings reinforce the critical role of RT-PCR as a gold standard diagnostic tool, particularly during the acute phase of illness or when serological results are inconclusive. Vaccination remains the cornerstone of mumps prevention, and there is an urgent need to incorporate the MMR vaccine into the UIP. Furthermore, targeted awareness campaigns, booster doses for older age groups, and enhanced surveillance systems are essential for addressing gaps in immunization and reducing the burden of mumps in India.