Mumps virus infection in vaccinated patients can be detected by an increase in specific IgG antibodies to high titres: a retrospective study

Abstract

Mumps outbreaks in highly vaccinated populations with genotype G have been reported repeatedly. Detection of these outbreaks can be difficult in a setting with relatively high vaccination coverage when acute cases of mumps are routinely diagnosed by IgM serology since this marker is not reliable for diagnosis of mumps re-infection. To learn whether diagnostic tests performed in a large private laboratory may be useful to detect mumps outbreaks retrospectively, we reviewed the results of almost 7000 mumps tests. Two groups were compared: group 1 comprised of 3438 samples from patients submitted by physicians and clinicians (it was assumed that these patients visited their doctor due to acute disease). Group 2 comprised of 3398 samples submitted from company medical officers and occupational physicians. Since these patients usually attend for routine check-ups and certification of immunity to vaccine-preventable diseases, these samples comprised a control group. From July 2010 to May 2011, a mumps virus outbreak with more than 300 cases occurred in Bavaria, Southeast Germany. Our study includes samples received for serological mumps tests from January 2009 until December 2011 (36 months). The two groups were analysed with regard to the number of IgM-positive cases per month and the level of IgG titre. We found a marked increase for both parameters in group 1 during the time of the outbreak, while the samples submitted by the occupational medical physicians did not display significant alterations. These parameters reflect the outbreak with high accuracy, indicating that a retrospective analysis of IgG titres may be a useful tool for detection of mumps outbreaks when, as was the case in Germany, (i) a nationwide notification system has not been implemented and (ii) a highly vaccinated population is affected.

Fig. 1.

Results of mumps virus (MuV) serology during 2009–2011. The outbreak period began in July 2010 and lasted until May 2011. Group 1 comprised samples submitted by practitioners and consultants in ambulatory and hospital settings, while group 2 comprised samples submitted by occupational medicine facilities. (a) Number of patients tested for presence of MuV-specific IgM antibodies. The samples of group 1 are presented above the x-axis, samples from occupational facilities below. (b) Number of patients showing MuV-specific IgG antibodies. The results of both groups are grouped in positive results (titres from 500 to 2500 GMT) and high positive titres (titres ⩾2500 GMT). Results of group 1 patients submitted by practitioners and consultants in ambulatory and hospital settings are indicated above the x-axis, while group 2 patients are given below the x-axis. (c) Correlation between top mumps IgG titres and time. The 5% of patients showing the highest MuV-specific IgG antibodies in groups 1 and 2, respectively, are indicated.

Fig. 2.

Box plot showing titres of IgG antibodies per month within the observation period. The outbreak period was from July 2010 to May 2011. Group 1 comprised patients of practitioners and consultants in ambulatory and hospital settings. Serum samples of group 2 patients were submitted from occupational medicine facilities.