NUR 603 Module 7 Outbreak Investigation Example

One Case, Three Lots, 749 Patients: An Outbreak Investigation of the 2012 Fungal Meningitis Outbreak

[Student Name]

Southern New Hampshire University

NUR 603: Epidemiology

Module Seven Outbreak Investigation

[Instructor Name]

[Date]

One Case, Three Lots, 749 Patients: An Outbreak Investigation of the 2012 Fungal Meningitis Outbreak

Most outbreaks that primary care clinicians encounter are small and local. The 2012 fungal meningitis outbreak was neither. It reached 20 states, affected hundreds of patients who had done nothing riskier than receive a routine injection for back pain and exposed weaknesses in the oversight of compounded drugs. It also illustrates, with unusual clarity, the logic of an outbreak investigation. This paper follows the investigation through its standard steps, calculates the key measures and argues that the outbreak's defining epidemiologic feature, a long and variable incubation period, shaped every decision about finding cases and protecting exposed patients.

Detecting the Outbreak

Outbreak investigations usually begin with an astute clinician or an unusual laboratory result rather than with surveillance data (Reingold, 1998). This one began in September 2012, when a Tennessee patient developed meningitis caused by Aspergillus fumigatus, a mold that almost never causes meningitis in a person with a normal immune system. The patient had received an epidural steroid injection weeks earlier. The Tennessee Department of Health quickly found further patients with meningitis at the same clinic, all of whom had received epidural injections of preservative-free methylprednisolone acetate prepared by a single compounding pharmacy in Massachusetts (Kainer et al., 2012). The first steps of any investigation, confirming the diagnosis and verifying that cases exceed what is expected, were straightforward here: the expected number of fungal meningitis cases after epidural injection is close to zero.

Defining a Case

A case definition sets the boundary of an investigation. In Tennessee, a case was a patient with fungal meningitis, posterior circulation stroke, spinal osteomyelitis or epidural abscess that developed after an epidural or paraspinal glucocorticoid injection (Kainer et al., 2012). The definition was broad in clinical terms because the infections presented in several forms, and it was tied to exposure because the exposure defined the population at risk. As the outbreak expanded, the national definition also came to include infections of peripheral joints after joint injections from the same lots. A definition that required laboratory confirmation would have missed most patients: fungal organisms were confirmed in only about 20% of cases nationally (Smith et al., 2013), because these molds are difficult to grow from spinal fluid.

Finding the Source

The shared exposure pointed to the product quickly, but analytic epidemiology tested it. In a cohort analysis among the 66 Tennessee case patients and the other exposed patients, the risk of infection increased with exposure to one particular lot, 06292012@26, with older vials, with higher doses, with multiple procedures and with a translaminar approach to epidural injection (Kainer et al., 2012). Each association supports a dose-response relationship with the contaminated product: more fungus delivered, or delivered closer to the spinal fluid, produced more infection. The pharmacy recalled three lots, and examination of unopened vials later found fungus, confirming the source in the laboratory (Smith et al., 2013). The predominant organism turned out to be Exserohilum rostratum, a black mold found in the environment and previously an almost unknown cause of human meningitis.

Measuring the Outbreak

The exposed population was unusually well defined, because facilities that received the recalled lots could identify every patient injected. By October 19, 2012, more than 99% of 13,534 potentially exposed people had been contacted. By July 1, 2013, 749 cases had been reported in 20 states, with 61 deaths (Smith et al., 2013). Table 1 shows the key measures.

Table 1. Key Measures of the 2012 Fungal Meningitis Outbreak

Note. Data from Smith et al. (2013), reported as of July 1, 2013. The attack rate uses all potentially exposed persons as the denominator.

The attack rate is best read as an average across exposures of differing intensity, since the Tennessee analysis showed that risk varied by lot, vial age, dose and technique. The case-fatality proportion was highest early, when the disease was unfamiliar and strokes were common: eight of the 66 Tennessee patients died, seven of whom had stroke (Kainer et al., 2012).

The Long Incubation Period and Case Finding

The feature that most shaped the response was time. The median interval from the last injection to diagnosis was 47 days, with a range from 0 to 249 days (Smith et al., 2013). Later in the outbreak, patients presented more often with epidural abscesses and other localized infections, sometimes without meningitis, and these developed later than strokes (Chiller et al., 2013). An epidemic curve for this outbreak would therefore continue for months after the recall, not because the source remained active but because exposed people were still passing through a long incubation. For that reason, investigators could not stop at notifying exposed patients once. They issued repeated guidance to clinicians to keep a low threshold for evaluating exposed patients with new headache or back pain, and many exposed patients underwent imaging and lumbar puncture even when symptoms were mild.

Control and Prevention

Control measures came in three layers. The recall and the closure of the pharmacy removed the source. That step came within days of the first report, before the organism had even been identified, which shows that control need not wait for every question to be answered. Notification of every exposed patient allowed early diagnosis and antifungal treatment; in Tennessee, 92% of patients received voriconazole (Kainer et al., 2012). Longer-term prevention required policy: Congress passed the Drug Quality and Security Act in 2013, which created a category of outsourcing facilities for compounded sterile drugs made in bulk and placed them under closer federal oversight. For advanced practice nurses, the lessons are practical: know where injectable drugs come from, report unusual infections promptly and recognize that the clinician who notices one strange case may be the start of the entire investigation.

Conclusion

The 2012 fungal meningitis outbreak moved from a single case of Aspergillus meningitis to 749 cases and 61 deaths across 20 states. A clear case definition, a cohort analysis showing dose-response and laboratory testing of unopened vials identified the source, while a long incubation period kept cases appearing for months and required sustained clinical vigilance. The investigation shows how each standard step, applied carefully, leads from one observation to national action.

References

Chiller, T. M., Roy, M., Nguyen, D., Guh, A., Malani, A. N., Latham, R., Peglow, S., Kerkering, T., Kaufman, D., McFadden, J., Collins, J., Kainer, M., Duwve, J., Trump, D., Blackmore, C., Tan, C., Cleveland, A. A., MacCannell, T., Muehlenbachs, A., . . . Jernigan, J. A. (2013). Clinical findings for fungal infections caused by methylprednisolone injections. New England Journal of Medicine, 369(17), 1610-1619. https://doi.org/10.1056/NEJMoa1304879

Kainer, M. A., Reagan, D. R., Nguyen, D. B., Wiese, A. D., Wise, M. E., Ward, J., Park, B. J., Kanago, M. L., Baumblatt, J., Schaefer, M. K., Berger, B. E., Marder, E. P., Min, J.-Y., Dunn, J. R., Smith, R. M., Dreyzehner, J., & Jones, T. F. (2012). Fungal infections associated with contaminated methylprednisolone in Tennessee. New England Journal of Medicine, 367(23), 2194-2203. https://doi.org/10.1056/NEJMoa1212972

Reingold, A. L. (1998). Outbreak investigations: A perspective. Emerging Infectious Diseases, 4(1), 21-27. https://doi.org/10.3201/eid0401.980104

Smith, R. M., Schaefer, M. K., Kainer, M. A., Wise, M., Finks, J., Duwve, J., Fontaine, E., Chu, A., Carothers, B., Reilly, A., Fiedler, J., Wiese, A. D., Feaster, C., Gibson, L., Griese, S., Purfield, A., Cleveland, A. A., Benedict, K., Harris, J. R., . . . Park, B. J. (2013). Fungal infections associated with contaminated methylprednisolone injections. New England Journal of Medicine, 369(17), 1598-1609. https://doi.org/10.1056/NEJMoa1213978