The Study
All surviving members of the 2012 outbreak in Jordan, their exposed contacts, and their household members who were identified serologically as either MERS-CoV positive or indeterminate were asked to consent to further participation. Participants were asked to provide a follow-up serologic specimen so we could compare 34-month results with 13-month results.
Specimens were prepared by the Jordan Central Public Health Laboratory (Amman, Jordan) and tested at the US Centers for Disease Control and Prevention (Atlanta, GA, USA). Antibody titers in serum samples were determined by an anti–MERS-CoV nucleocapsid indirect ELISA and by MERS-CoV (Hu/Jordan-N3/2012 strain) indirect IFA.[1] The presence of neutralizing antibody titers was determined by microneutralization with live MERS-CoV (Hu/Jordan-N3/2012 strain) in a Biosafety Level 3 laboratory as described previously.[1] Neutralization titers were defined as the reciprocal of the highest serum dilution completely protecting the Vero cell monolayer from cytopathic effect in at least 1 of 3 parallel wells. Titers >1:20 were reported as positive.
Of the 15 surviving persons with >1 positive serologic test result, 13 (87%) consented to follow-up testing. All 7 (100%) surviving persons with >2 positive serologic test results 13 months after the MERS-CoV outbreak also consented. Each of these 7 persons was considered to be a probable MERS-CoV case-patient according to World Health Organization criteria; each had had a symptomatic acute respiratory infection during the outbreak period and documented, unprotected exposure to >1 person with a case confirmed by reverse transcription PCR.
For the 7 probable case-patients, ELISA titers at 34 months ranged from <400 to 1,600, representing reduced antibody titers compared with the 13-month estimates (400–6,400) for all but 1 person (Table). A nurse who worked in an intensive care unit (participant 06) and cared for confirmed case-patients during the outbreak was the only participant for whom ELISA indicated a consistent titer of 1,600 at both times.
Of these 7 participants, 6 (86%) had neutralizing antibody titers ranging from 20 to 80 at the 34-month follow-up evaluation, and only 2 (29%) had any decrease in neutralizing antibody titers over time. One participant had no detectable neutralizing antibodies (Figure). Of the 7 participants for whom IFA results were positive at 13 months, 4 (57%) had positive results at 34 months.
Figure.
Neutralizing antibody titers against Middle East respiratory syndrome coronavirus (Hu/Jordan-N3/2012 strain) among 7 surviving case-patients at 13 and 34 months after the 2012 outbreak in Jordan. Patient numbers match those in the Table.
For the 8 surviving participants whose serologic results at 13 months were indeterminate, 6 (75%) consented to further testing. Of these, 3 (50%) reported having had no respiratory symptoms, 1 reported having had mild respiratory symptoms, and 2 had been hospitalized with respiratory infections; all 6 had had documented, unprotected exposure to >1 case-patient. Each of these 6 persons had negative serologic test results at 34 months and continue to be considered negative overall.
Emerging Infectious Diseases. 2016;22(10):1824-1826. © 2016 Centers for Disease Control and Prevention (CDC)
