D401 Task 1 Outbreak Analysis Example

Two Centers, One Virus: An Epidemiological Analysis of a Hand, Foot and Mouth Disease Outbreak at Two Child Care Centers in a Composite Town

Student Name

Leavitt School of Health, Western Governors University

D401: Introduction to Epidemiology, Task 1

Course Instructor

Month Day, Year

Two Centers, One Virus: An Epidemiological Analysis of a Hand, Foot and Mouth Disease Outbreak at Two Child Care Centers in a Composite Town

The Outbreak

In late August, the county health department in the composite town of Harlow Falls received reports of hand, foot and mouth disease (HFMD) from two licensed child care centers. HFMD is a common childhood illness caused by nonpolio enteroviruses, most often coxsackievirus A16, coxsackievirus A6 and enterovirus A71. It usually produces fever, painful sores in the mouth and a rash on the palms and soles, and most children recover within a week to ten days, although some strains can cause neurological complications (Esposito & Principi, 2018).

Maplewood Early Learning enrolls 80 children from 6 weeks to 5 years old and employs 16 staff. Its rooms are organized by family groups, so infants, toddlers and preschoolers share space for most of the day. Riverside Children's Center enrolls 60 children and employs 12 staff, and its rooms are separated by age: an infant room, a toddler room of 14 children and two preschool rooms. Both centers adopted the same control measure when the first cases were confirmed: a child diagnosed with HFMD was sent home and could not return for 7 days after diagnosis.

Over five weeks, the centers reported the cases shown below. Because the centers are different sizes, the table uses attack rates (the share of each group that fell ill) instead of raw counts.

Two Risk Factors Common to Both Centers

The first risk factor is diapering and toileting support for young children. Enteroviruses are shed in stool, and fecal shedding lasts far longer than the illness itself. In a study that followed 34 patients with enterovirus A71 infection, viral RNA was found in stool for as long as 42 days after onset, while shedding from the throat lasted up to 24 days (Han et al., 2010). Every diaper change in either center is a possible exposure for staff hands, changing surfaces and, through those hands, other children. Both centers care for children in diapers, so both carried this risk from the start.

The second risk factor is shared objects that go into children's mouths. Toddlers mouth toys, share cups when adults are not watching and touch their faces constantly. Respiratory secretions and fluid from blisters also carry the virus (Esposito & Principi, 2018). A toy mouthed by an infected child in the morning can be picked up by another child an hour later. Both centers use shared toy bins, and neither had a routine of removing mouthed toys for sanitizing before the outbreak.

Two Patterns That Differ Between the Centers

Pattern one: the outbreak at Maplewood spread across every room, while Riverside's stayed in one. At Maplewood, cases appeared in all four family rooms within the first two weeks. At Riverside, all nine cases were toddlers, and none occurred in the infant or preschool rooms. The likely explanation is the difference in how children are grouped. Mixed-age rooms at Maplewood put children of every age in contact with each other and with every staff member, so the virus had many paths between groups. Riverside's age-separated rooms, with their own staff, own diaper stations and own toys, created natural barriers. Inside the toddler room, however, the attack rate was very high, 64.3%, which fits a group of children who are both mouthing objects and still in diapers.

Pattern two: Maplewood staff became ill and Riverside staff did not. Four of 16 Maplewood employees developed symptoms, an attack rate of 25%, compared with none of 12 at Riverside. One plausible explanation is that Maplewood staff float between rooms and change diapers for children of all ages, so each worker was exposed to more infected children over a longer period. Adults are often infected with few or no symptoms, so the four ill staff may represent only part of the infections among adults (Esposito & Principi, 2018). An adult with a mild or silent infection who continues working could carry the virus between rooms, which would help explain why Maplewood's outbreak lasted 34 days compared with 12 at Riverside.

How the Two Outbreaks May Be Connected

The health department's line list shows that Riverside's first case, a 2-year-old, has a 4-year-old sister enrolled at Maplewood who became ill five days earlier. The median incubation period of HFMD in young children is about 4.4 days (Yang et al., 2017), so a household exposure from the sister fits the timing. This connection matters because it suggests one outbreak moving between two centers through a family, rather than two separate introductions.

Gaps in the Evidence

Three gaps limit this analysis, and each would answer a specific question.

First, laboratory typing of the virus. The reports are based on clinical diagnosis, and no specimens were tested to identify the enterovirus type. Typing samples from both centers would show whether the outbreaks share one strain, which would confirm the sibling link, and would tell the health department whether enterovirus A71, the type linked to severe neurological disease, is circulating (Esposito & Principi, 2018).

Second, exposure records for staff. The centers did not record which rooms each staff member worked in on each day. A simple staffing log, matched against case onset dates, would test whether floating staff carried the virus between Maplewood's rooms, which is the main explanation offered for the first pattern.

Third, symptom and absence data for household contacts. Only children and staff who were diagnosed are counted. Knowing which siblings and parents became ill, and when, would show how much transmission occurred at home rather than at the centers, and whether other family links like the one between the two sisters exist.

Was Excluding Children for 7 Days Effective?

The exclusion policy was only partly effective, and the difference between the centers shows why.

At Riverside, cases stopped 12 days after the first one. Because the virus stayed in one room, sending sick toddlers home, together with the room's separate staff and supplies, removed the most infectious children from a closed group. Exclusion probably helped there, although the toddler room had already reached a very high attack rate before it took effect.

At Maplewood, new cases continued for more than three weeks after the policy began. Three features of the disease explain this. Children are infectious before their rash appears, so by the time a case was diagnosed and sent home, classmates had already been exposed. Children who returned after 7 days were still shedding virus in stool; in one study, enterovirus A71 was found in feces for as long as 54 days (Li et al., 2013). And adults with mild or silent infections were never excluded at all. A policy that removes only visibly sick children for a week cannot interrupt a virus that spreads before symptoms, after symptoms and without symptoms.

The policy also carried costs. Each exclusion meant a week of missed work for a parent, and families under that pressure may be less likely to report mild symptoms. Exclusion therefore had limited benefit at Maplewood and some risk of hiding cases.

Recommendation

For the rest of this outbreak and any future one, the centers should rely on measures that work whether or not a child looks sick. Staff should wash hands with soap and water after every diaper change and before handling food, since alcohol-based sanitizer is less effective against nonenveloped viruses like enteroviruses. Mouthed toys should be removed and cleaned before another child uses them. Maplewood should assign staff to fixed rooms for the duration of an outbreak, which would test the floating-staff explanation and protect children at the same time. Children should stay home while they have a fever or are drooling from mouth sores, and then return, since a fixed 7-day exclusion does not end shedding. Finally, specimens should be sent for typing, so that the health department knows which virus it is dealing with. Because the incubation period can exceed 10 days in a minority of children (Yang et al., 2017), these measures should continue for at least two weeks after the last case before the outbreak is declared over.

References

Esposito, S., & Principi, N. (2018). Hand, foot and mouth disease: Current knowledge on clinical manifestations, epidemiology, aetiology and prevention. European Journal of Clinical Microbiology & Infectious Diseases, 37(3), 391-398. https://doi.org/10.1007/s10096-018-3206-x

Han, J., Ma, X.-J., Wan, J.-F., Liu, Y.-H., Han, Y.-L., Chen, C., Tian, C., Gao, C., Wang, M., & Dong, X.-P. (2010). Long persistence of EV71 specific nucleotides in respiratory and feces samples of the patients with hand-foot-mouth disease after recovery. BMC Infectious Diseases, 10, Article 178. https://doi.org/10.1186/1471-2334-10-178

Li, J., Lin, C., Qu, M., Li, X., Gao, Z., Zhang, X., Liu, Y., Huang, Y., Wang, X., Jia, L., Li, X., Liu, G., Yan, H., Chen, L., & Wang, Q. (2013). Excretion of enterovirus 71 in persons infected with hand, foot and mouth disease. Virology Journal, 10, Article 31. https://doi.org/10.1186/1743-422X-10-31

Yang, Z., Zhang, Q., Cowling, B. J., & Lau, E. H. Y. (2017). Estimating the incubation period of hand, foot and mouth disease for children in different age groups. Scientific Reports, 7, Article 16464. https://doi.org/10.1038/s41598-017-16705-7