APMIS 114: 788–94, 2006 C 2006 The Authors Printed in Denmark . All rights reserved Journal Compilation C 2006 APMIS ISSN 0903-4641 Sensitivity and specificity of immunoglobulin G titer for the diagnosis of mumps virus in infected patients depending on vaccination status JUAN CARLOS SANZ, 1 MARI ´ A DEL MAR MOSQUERA, 2 JUAN EMILIO ECHEVARRI ´ A, 2 MARISA FERNA ´ NDEZ, 1 NIEVES HERRANZ, 1 GUSTAVO PALACIOS 3 and FERNANDO DE ORY 2 1 Laboratorio Regional de Salud Pu ´ blica, Instituto de Salud Pu ´ blica de la Comunidad de Madrid, 2 Servicio de Microbiologı ´a Diagno ´stica, Centro Nacional de Microbiologı ´a, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain, and 3 Jerome L. and Dawn Greene Infectious Diseases Laboratory, Columbia University, NY, USA Sanz JC, Mosquera MM, Echevarrı ´a JE, Ferna ´ndez M, Herranz N, Palacios G, De Ory F. Sensitivity and specificity of immunoglobulin G titer for the diagnosis of mumps virus in infected patients de- pending on vaccination status. APMIS 2006;114:788–94. The aim of the study was to evaluate the usefulness of serological detection of mumps IgM and titration of IgG in patients with acute parotitis according to their vaccination status. The detection of mumps virus RNA in saliva by RT-PCR was used as reference. 116 patients (109 of them previously vaccinated) with mumps RT-PCR-negative results and 21 (19 vaccinated) with mumps RT-PCR-posi- tive results were studied. Mumps-specific IgM and IgG were assayed by EIA (Enzygnost, Dade Behring, Germany). IgM results were expressed as positive or negative. For IgG, several cut-offs were calculated using receiver operating characteristic (ROC) curves. Seven RT-PCR-positive and five RT- PCR-negative patients showed IgM-positive results (sensitivity 33.3% and specificity 95.7%). Among vaccinated patients, the sensitivity and specificity of IgM were 26.3% (5/19) and 99.1% (108/109). For IgG, a titer of 5,000 in all the patients showed a sensitivity of 76.2% (16/21) and a specificity of 83.6% (97/116). In vaccinated patients, the corresponding figures for this cut-off were 84.2% (16/19) and 83.5% (91/109), respectively. Although IgM detection against mumps is highly specific, its sensitivity is very low in immunized subjects. In this group, the titration of IgG could serve as an additional diagnostic tool. Key words: Mumps; IgM; IgG; serology; vaccine. Fernando De Ory, Servicio de Microbiologı ´a Diagno ´stica, Centro Nacional de Microbiologı ´a, Institu- to de Salud Carlos III, Madrid, Spain. e-mail: fory/isciii.es An increase in the notification of cases and out- breaks of mumps virus infections has been ob- served in Spain (1, 2) and other European coun- tries (3) during recent years. Low vaccination coverage, inadequate vaccination scheduling, and combinations of primary and secondary Received 9 March 2006. Accepted 14 July 2006. 788 vaccine failure have been proposed as possible causes for the reemergence of this disease (4). Despite the increase in the incidence of mumps, only a small proportion of suspected cases are confirmed by specific IgM determi- nation. Some virological and immunological features of this infection have made serological diagnosis in vaccinated populations cumber- some and inconclusive: (a) Immunogenicity against mumps is not