Underestimation of Invasive Meningococcal Disease in Italy

Abstract

Knowing the incidence of invasive meningococcal disease (IMD) is essential for planning appropriate vaccination policies. However, IMD may be underestimated because of misdiagnosis or insufficiently sensitive laboratory methods. Using a national molecular surveillance register, we assessed the number of cases misdiagnosed and diagnoses obtained postmortem with real-time PCR (rPCR), and we compared sensitivity of rPCR versus culture-based testing. A total of 222 IMD cases were identified: 11 (42%) of 26 fatal cases had been misdiagnosed or undiagnosed and were reclassified as IMD after rPCR showed meningococcal DNA in all available specimens taken postmortem. Of the samples tested with both rPCR and culture, 58% were diagnosed by using rPCR alone. The underestimation factor associated with the use of culture alone was 3.28. In countries such as Italy, where rPCR is in limited use, IMD incidence may be largely underestimated; thus, assessments of benefits of meningococcal vaccination may be prone to error.

Keywords: Italy; Neisseria meningitidis; PCR; bacteria; bacterial meningitis; invasive meningococcal disease; misdiagnosis; underestimation; underreporting.

Figure 1

Distribution of patients diagnosed with invasive meningococcal disease during hospitalization or postmortem evaluation, by test performed for Neisseria meningitidis (real-time PCR [rPCR] or rPCR and culture), from a national register for molecular surveillance of invasive bacterial disease, Italy, 2007–2014.

Figure 2

Age distribution of 222 patients diagnosed with invasive meningococcal disease, from a national register for molecular surveillance of invasive bacterial disease, Italy, 2007–2014.