Mumps outbreaks have been a frequent topic covered here on Outbreak Thursday. We have previously chronicled the rise in mumps incidence in the US, the quarantine of a US Navy ship due to a mumps outbreak, and mumps outbreaks in migrant detention facilities. This week, we are pleased to share newly published results from a recent observation. Outbreak Observatory conducted in partnership with the Chester County Health Department (Pennsylvania, USA) to learn from their operational experience battling a mumps outbreak in a local immigrant population in 2018. Our goals were not only to improve the operational knowledge about how to control the spread of this vaccine-preventable disease, but also to identify the factors that can improve or inhibit response to outbreaks of mumps and other infectious diseases.

Mumps Outbreaks

With the introduction of the 2-dose MMR vaccine in 1989, mumps incidence in the US decreased by more than 99%, down to only a few hundred cases per year through the early 2000s. Recent years, however, have exhibited a worrying trend. Sizable outbreaks in 2006 (6,584 cases), 2009 (1,991 cases), and 2010 (2,612 cases) foretold of a growing mumps threat. Mumps incidence in the US has exceeded 1,000 cases every year since 2014, including a major epidemic in 2016-17, which resulted in more than 12,000 total cases nationwide. The US CDC reported 2,363 cases across 47 states and Washington, DC from January 1 to September 13, 2019. While mumps is a vaccine-preventable illness, low vaccination coverage and waning immunity from childhood immunizations may be contributing to rising incidence.

Mumps in Chester County, Pennsylvania

In 2018, health department officials in Chester County, Pennsylvania, responded to a multi-jurisdictional mumps outbreak that primarily affected a local immigrant community, some of whom spoke little or no English. Additionally, some did not have health insurance or official immigration documentation. The outbreak originated across state lines, at a large festival that resulted in mumps cases in several states. Chester County reported a total of 39 suspected or confirmed mumps cases, and an additional 22 suspected or confirmed cases were reported in 2 neighboring jurisdictions.

The health department was concerned that many in the at-risk population were likely unvaccinated, as they emigrated from countries in Latin America that did not implement widespread mumps elimination programs until the early- to mid-1990s. Additionally, the outbreak was identified in the weeks leading up to the Easter holiday, and there was concern that holiday gatherings could increase the risk of transmission. The health department felt that these factors necessitated an urgent response, and health officials rapidly implemented a variety of public health interventions. One key component of the response was vaccination, conducted at 2 local mushroom farms where several cases and their close contacts worked. The health department partnered with La Comunidad Hispana (LCH), a federally qualified health center (FQHC) that serves the affected community, to engage the at-risk population and implement the vaccination operations.

Outbreak Response Challenges

Insurance and immigration status for affected individuals posed significant barriers to the outbreak response. In the affected community, insurance coverage was often viewed as a proxy for immigration status, as undocumented immigrants were often unable to obtain health insurance. Some cases and their contacts may have been deterred from seeking care, because healthcare providers and the health department were required to inquire about health insurance status, prompting fear that they would be identified as undocumented immigrants and reported to immigration officials. Additionally, some healthcare providers were hesitant to order laboratory tests or report potential mumps cases among uninsured individuals due to concern that their patients could be reported to immigration authorities. The health department does not collect or report immigration status as part of its outbreak response protocols, but other governmental social service programs do inquire about immigration status, which may have created a misperception among some individuals regarding the purpose behind obtaining insurance status. Health department personnel felt that the lack of timely and accurate information from healthcare providers associated with these concerns complicated surveillance, case investigations, contact tracing, and the subsequent treatment of patients.

Vaccinating case contacts and other at-risk individuals also proved to be challenging. The health department had well-established mass vaccination plans and prior experience conducting vaccination point-of-dispensing (POD) operations through annual seasonal influenza vaccination clinics. Despite their planning and experience, however, vaccination operations for the mumps outbreak was complicated by a need to consider patients’ insurance status. Principally, the health department was unable to procure enough vaccine doses to support the outbreak response. Chester County requested vaccine via a Section 317 federal immunization grant, but state officials stipulated that the federally funded vaccine could only be used for uninsured individuals. To secure additional vaccine for insured individuals, the health department partnered with LCH, which was able to submit for insurance reimbursement for the vaccinations. At the vaccination POD, individuals were screened for health insurance status, with uninsured individuals vaccinated by health department personnel and insured individuals vaccinated by LCH staff. In the end, LCH purchased 200 MMR doses on the private market but used less than half for the outbreak. The health department administered 93 vaccinations to uninsured individuals.

Another important challenge was the need to facilitate bilingual health communication and education for the affected community. The health department utilized their own interpreters and bilingual nurses to communicate with the immigrant community during case investigations and vaccination clinic operations, but their local resources were limited. Interpreters were not specifically assigned to the outbreak response, and they were not always available, which slowed case investigations. Increased access to dedicated interpretation/translation services to support the outbreak response would have been a valuable resource that could have improved the efficiency of case investigations and promoted more culturally competent public messaging.

Though relatively small in terms of total cases, the outbreak proved to be costly to both the health department and LCH. In total, the up-front cost of outbreak response operations exceeded $35,000. For LCH, the largest outbreak response-associated expenditure was the vaccine purchase. While LCH did submit insurance claims for the vaccinations they administered at the POD, most claims were rejected because LCH was not listed as the primary care provider for those individuals, limiting their ability to recover the cost of the purchased vaccines. From the health department’s perspective, most of the cost incurred was due to staff time. Ultimately, only about $5,000 in vaccine costs were reimbursed by insurance companies, resulting in a net cost of approximately $30,000 for this outbreak response.

Broader Implications

Chester County’s mumps experience demonstrates important lessons for responding to infectious disease outbreaks, particularly those occurring in hard-to-reach populations. Undocumented immigrant communities have unique needs and vulnerabilities, including language and cultural barriers and potentially concerns about immigration status. Partnerships with organizations and individuals with existing ties to these communities and appropriate cultural understanding are critical to supporting response operations. Fortunately, Chester County’s health department had already established a number of important capabilities and capacities in advance of the outbreak—including partnerships with community organizations, in-house language capabilities, and regularly exercised mass vaccination plans. Without these functions, programs, and policies already in place, the response to this outbreak would likely have been much less effective.

This mumps outbreak also demonstrated the financial and logistical burdens that even small outbreaks can pose on health departments and partnering organizations. At 39 cases, Chester County’s response required and up-front cost of nearly $1,000 per case (and still more than $750 per case after insurance reimbursement). Had the outbreak been larger or involved more severe outcomes, the response could have been much more difficult and expensive. When Chester County was unable to obtain sufficient vaccine for insured individuals, it was fortunate that LCH was able to purchase the necessary doses on the private market (and absorb the cost due to rejected insurance claims). But not every jurisdiction has such advantages. Despite the public health benefits of developing and maintaining outbreak response capacities and capabilities, including mass vaccination, these resources are not present in all jurisdictions. For them, additional planning and funding may be required.

Photo courtesy of CDC/ Dr. F. A. Murphy.
Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.