Successful contact tracing systems for COVID-19 rely on effective quarantine and isolation.

Models of contact tracing often over-simplify the effects of quarantine and isolation on disease transmission. We develop a model that allows us to investigate the importance of these factors in reducing the effective reproduction number. We show that the reduction in onward transmission during quarantine and isolation has a bigger effect than tracing coverage on the reproduction number. We also show that intuitively reasonable contact tracing performance indicators, such as the proportion of contacts quarantined before symptom onset, are often not well correlated with the reproduction number. We conclude that provision of support systems to enable people to quarantine and isolate effectively is crucial to the success of contact tracing.

Elevated procalcitonin as a diagnostic marker in meningococcal disease.

Patients with meningococcal disease who seek medical attention can create a diagnostic dilemma for clinicians due to the nonspecific nature of the disease's presentation. This study assesses the diagnostic accuracy of procalcitonin levels in the setting of meningococcal disease. Two emergency department cohorts (A and B) were studied between 2002 and 2005, during the current epidemic of serogroup B meningococcal disease in New Zealand. Cohort A consisted of 171 patients, all with confirmed meningococcal disease (84 children, 87 adults). Cohort B consisted of a large (n=1,524) consecutively recruited population of febrile patients who presented to the emergency department, 28 of whom had confirmed meningococcal disease. Within the meningococcal disease cohort (cohort A), the geometric mean procalcitonin level was 9.9 ng/ml, with levels being higher in children than in adults (21.6 vs. 4.6 ng/ml, p=0.01). The overall sensitivity of elevated procalcitonin, using a cutoff of 2.0 ng/ml in children and 0.5 ng/ml in adults, was 0.93 (95%CI: 0.88-0.96). Despite the higher cutoff level for paediatric patients, a trend towards greater sensitivity existed in children (0.96 vs. 0.90; p=0.08). Elevated procalcitonin was correlated with whole blood meningococcal load (r=0.50) and Glasgow Meningococcal Sepsis Prognostic Score (r=0.40). Within the cohort of patients who were febrile on presentation (cohort B), the specificity of elevated procalcitonin in meningococcal disease was 0.85 (95% CI: 0.83-0.87), the positive and negative likelihood ratios were 6.1 and 0.08, respectively, and the sensitivity of elevated procalcitonin (0.93; 95% CI: 0.76-0.99) was corroborated. Measurement of procalcitonin is a useful tool in patients with nonspecific febrile illnesses when the possibility of meningococcal disease is present. The diagnostic accuracy surpasses that of current early laboratory markers, allowing results to be used to guide decisions about patient management.