Culture and Real-time Polymerase Chain reaction sensitivity in the diagnosis of invasive meningococcal disease: Does culture miss less severe cases?

Abstract

BackgroundInvasive meningococcal disease (IMD) is a highly lethal disease. Diagnosis is commonly performed by culture or Realtime-PCR (qPCR).AimsOur aim was to evaluate, retrospectively, whether culture positivity correlates with higher bacterial load and fatal outcome. Our secondary aim was to compare culture and qPCR sensitivity.MethodsThe National Register for Molecular Surveillance was used as data source. Cycle threshold (CT), known to be inversely correlated with bacterial load, was used to compare bacterial load in different samples.ResultsThree-hundred-thirteen patients were found positive for Neisseria meningitidis by qPCR, or culture, or both; 41 died (case fatality rate 13.1%); 128/143 (89.5%) blood samples and 138/144 (95.8%) CSF were positive by qPCR, 37/143 (25.9%) blood samples and 45/144 (31.2%) CSF were also positive in culture. qPCR was 3.5 times (blood) or 3.1 times (CSF) more sensitive than culture in achieving a laboratory diagnosis of IMD (OR 24.4; 95% CI 12.2–49.8; p < .10−4; Cohen’s κ 0.08 for blood and OR 49.0; 95% CI 19.1–133.4; p<10−4; Cohen’s κ 0.02; for CSF). Positivity of culture did not correlate with higher bacterial loads in blood (mean CT 27.7±5.71, and CT 28.1±6.03, p = 0.739 respectively in culture positive or negative samples) or in CSF (mean CT 23.1±4.9 and 24.7±5.4 respectively in positive or negative CSF samples, p = 0.11).CT values in blood from patients who died were significantly lower than in patients who survived (respectively mean 18.0, range 14–23 and mean 29.6, range 16–39; p<10−17). No deaths occurred in patients with CT in blood over 23. Positive blood cultures were found in 10/25 (40%) patients who died and in 32/163 (19.6%) patients who survived, p = 0.036, OR 2.73; 95% CL 1.025–7.215), however 60% of deaths would have remained undiagnosed with the use of culture only.ConclusionsIn conclusion our study demonstrated that qPCR is significantly (at least 3 times) more sensitive than culture in the laboratory confirmation of IMD. The study also demonstrated that culture negativity is not associated with lower bacterial loads and with less severe cases. On the other side, in patients with sepsis, qPCR can predict fatal outcome since higher bacterial load, evaluated by qPCR, appears strictly associated with most severe cases and fatal outcome. The study also showed that molecular techniques such as qPCR can provide a valuable addition to the proportion of diagnosed and serotyped cases of IMD.

A pooled analysis of the LAMP assay for the detection of Neisseria meningitidis

“…Clinical detection of Neisseria meningitidis in many countries currently uses PCR, ELISA, and bacterial culture,[ 9 ] and PCR is considered the most authoritative standard. However, these technologies have limited applicability in poor and developing countries.…”

Invasive Meningococcal Disease in Italy: from the analysis of national data to an evidence-based vaccination strategy.

“…One reason that could explain the increase in IMDs is the peak of cases recorded in Tuscany in 2015 and 2016, especially in adolescents and young adults [ 40 , 43-45 ] and in Liguria in 2016 and 2017 [ 40 , 41 ]. Moreover, there have also been improvements in the laboratory diagnosis confirmation system, both at regional and national level [ 33 ]. For example, in Tuscany during 2015, real-time polymerase chain reaction (PCR), a more sensitive, rapid and accurate laboratory diagnostic test [ 33 ], was made available to all hospitals by a regional law [ 46 ], reducing the underestimation of IMD [ 29 ] and consequently improving the accuracy of the surveillance system and differentiating IBIs [ 29 , 33 , 47 ].…”

Diagnostic accuracy of the LAMP assay for Neisseria meningitidis

“…The clinical detection of Neisseria meningitidis in many countries currently uses PCR, ELISA, and bacterial culture [8] , and PCR is considered the most authoritative standard. However, these technologies have limited applicability in poor and developing countries.…”