MERS Serosurveys: Waning Antibody Levels Complicate Epidemiologic Surveillance
Amesh A. Adalja, MD, FACP, FACEP, FIDSA, May 12, 2017
With every infectious disease, there is a spectrum of illness that can range from fulminant fatal disease to completely asymptomatic disease. This range makes epidemiologic studies difficult, as case counts and transmission dynamics can become complicated with unrecognized cases and nonapparent chains of transmission. These factors are crucially important for emerging infectious diseases for which understanding the trajectory of spread is vital. One current emerging infectious disease outbreak that illustrates these points is Middle East Respiratory Syndrome (MERS). To date, MERS has infected nearly 2,000 people in 29 countries, killing almost 700. Understanding the true burden of this pathogen, and understanding its spread and transmission, should remain a high priority.
A new paper on the 2015 travel-related spread of the zoonotic emerging infectious disease MERS to South Korea, where 186 cases with 36 deaths occurred, provides insight into the immunological evidence that MERS-CoV left in some of the individuals infected there.
Antibody Titers Studied Over the Course of a Year
In this study, Choe and colleagues studied 11 patients admitted to Seoul National University Hospital. Severe clinical disease occurred in 5, while mild disease occurred in 6. Sampling of serum occurred at approximately 6 months and 12 months post-infection.
In those with severe disease, all had neutralizing antibody titers ≥40 at 1 year. By contrast, only a third of those with mild disease had antibody titers that met this threshold. Antibody titers were also seen to diminish over time. When tested with ELISA, those with mild disease had negative results.
Implications for Serosurveys
The kinetics of antibody products post-MERS infection has important implications for epidemiologic surveillance. Often, to establish a prevalence rate in a population, serosurveys are undertaken to determine the level of antibody in a population to a particular microbe. If, as demonstrated by Choe and colleagues, MERS antibody levels decline after mild infections (even in those requiring hospitalization), retrospective serosurveys will potentially miss many cases. Such a phenomenon could provide a grossly altered picture of the true nature of an outbreak and influence policy decisions regarding preparedness.
Choe PG, Perera RAPM, Park WB, et al. MERS-CoV antibody responses 1 year after symptom onset, South Korea, 2015. Emerg Infect Dis 2017;23(7).
https://dx.doi.org/10.3201/eid2307.170310. Accessed May 10, 2017.