Measles outbreak in Illinois underscores critical need for vaccination

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In a recent study published in the Morbidity and Mortality Weekly Report (MMWR), researchers from Illinois, the United States of America (US), reported the incidence of five measles cases among unvaccinated children who resided in the same building but did not socialize with each other.

Notes from the Field: Measles Outbreak — Cook County, Illinois, October–November 2023. Image Credit: adriaticfoto / ShutterstockNotes from the Field: Measles Outbreak — Cook County, Illinois, October–November 2023. Image Credit: adriaticfoto / Shutterstock


Measles is an infectious disease preventable by vaccination and poses a significant health risk. In the US, it is advised that children receive two doses of the measles, mumps, and rubella (MMR) vaccine, typically administered between the ages of 12 and 15 months and again between 4 and 6 years. The present study describes a concerning case of measles outbreak among five unvaccinated children from two families residing in the same building who did not socialize with each other.

The case

On October 5, 2023, Patient A, a 2-year-old immigrant from Yemen, was diagnosed with an unspecified viral illness at the emergency department (ED) of Hospital A, following negative test results for influenza, coronavirus disease 2019 (COVID-19), and respiratory syncytial virus. Patient A had not been administered the MMR vaccine and had symptoms of fever, cough, and coryza. On October 8, Patient A visited Hospital B's ED due to exacerbated respiratory symptoms and tested positive for rhinovirus/enterovirus. Patient A was then admitted again to Hospital A for respiratory distress.

Notably, Patient A developed a maculopapular rash while hospitalized the next day. On October 10, the family disclosed that they had been in contact with an individual diagnosed with measles before entering the US. Measles was confirmed via real-time reverse transcription-polymerase chain reaction (RT-PCR), and the patient was discharged.


Between October 5 and 11, the child was potentially exposed to 247 healthcare workers and 177 patients and kin. This included 13 infants aged under one year, five immunocompromised children, and one unvaccinated child aged over one year. Two of these children were given the MMR vaccine within three days of exposure, while 13 received immune globulin as a precautionary measure.

Patient A's domestic contacts included two siblings who had not received the MMR vaccine and were found to be susceptible to measles through serologic testing. The siblings were Patient B, aged four years and Patient C, aged nine. The siblings contracted measles during quarantine, with varied symptoms. Although patient B required an ED visit for supportive care, neither child was hospitalized. All the residents of the building were alerted on October 17.

On October 30, Patient D (another child aged two years) visited the ED with symptoms and resided on a different floor of the same building as Patient A. The child had not received the MMR vaccine, as its parents objected based on concerns about the side effects of the vaccine. Measles was confirmed through RT-PCR.

Interestingly, despite living in the same building, the families of both sets of patients had different cultural backgrounds and languages. Both families denied having any contact with each other. While their apartment units did not share ventilation, they shared laundry facilities and building entrances.

On October 31, Patient D's unvaccinated one-year-old sibling, named Patient E, was tested due to isolated coryza. The child attended a child-care facility on October 30 while symptomatic and confirmed measles through RT-PCR. Post-exposure prophylaxis was administered to susceptible individuals, including immune globulin for one child and an early second dose of MMR vaccine for others. Patient E did not develop a fever until November 6, and a rash appeared on November 9, nine days after the positive test result and notification of the child-care facility.

While testing for measles is typically done when prodromal symptoms occur, such as cough, fever, coryza, or conjunctivitis, the isolated coryza experienced by Patient E may not have been measles-related. As measles testing before fever onset is uncommon, determining the accurate contagious period for this patient was challenging. Patient E did not need hospitalization.


Five children contracted measles in this outbreak. They were unvaccinated despite being eligible for the MMR vaccine owing to cultural barriers, limited access to healthcare, and vaccine refusal. Outbreaks have been observed previously among close-knit communities, but the present families were not a part of such networks. Public health responses typically involve tailored approaches, like culturally appropriate education materials and translation services. However, these efforts are expensive and time-consuming. This outbreak highlights measles' high contagiousness, even among children not in each other's contact.


In conclusion, the study emphasizes the need for all children and susceptible individuals to receive two doses of the MMR vaccine at appropriate intervals. Clinicians should suspect measles in patients with febrile rash illness and ensure vaccination to prevent future outbreaks.

Journal reference:
  • Notes from the Field: Measles Outbreak — Cook County, Illinois, October–November 2023. Bemis K. et al., MMWR Morbidity and Mortality Weekly Report, 73:229–230 (2024), DOI: 10.15585/mmwr.mm7310a3,
Dr. Sushama R. Chaphalkar

Written by

Dr. Sushama R. Chaphalkar

Dr. Sushama R. Chaphalkar is a senior researcher and academician based in Pune, India. She holds a PhD in Microbiology and comes with vast experience in research and education in Biotechnology. In her illustrious career spanning three decades and a half, she held prominent leadership positions in academia and industry. As the Founder-Director of a renowned Biotechnology institute, she worked extensively on high-end research projects of industrial significance, fostering a stronger bond between industry and academia.  


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