The role of super-spreading events in Mycobacterium tuberculosis transmission: evidence from contact tracing

Melsew, Yayehirad A., Gambhir, Manoj, Cheng, Allen C., McBryde, Emma S., Denholm, Justin T., Tay, Ee Laine, and Trauer, James M. (2019) The role of super-spreading events in Mycobacterium tuberculosis transmission: evidence from contact tracing. BMC Infectious Diseases, 19. 244.

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Background: In current epidemiology of tuberculosis (TB), heterogeneity in infectiousness among TB patients is a challenge, which is not well studied. We aimed to quantify this heterogeneity and the presence of super-spreading events that can assist in designing optimal public health interventions.

Methods: TB epidemiologic investigation data notified between 1 January 2005 and 31 December 2015 from Victoria, Australia were used to quantify TB patients' heterogeneity in infectiousness and super-spreading events. We fitted a negative binomial offspring distribution (NBD) for the number of secondary infections and secondary active TB disease each TB patient produced. The dispersion parameter, k, of the NBD measures the level of heterogeneity, where low values of k (e.g. k<1) indicate over-dispersion. Super-spreading was defined as patients causing as many or more secondary infections as the 99th centile of an equivalent homogeneous distribution. Contact infection was determined based on a tuberculin skin test (TST) result of 10mm. A NBD model was fitted to identify index characteristics that were associated with the number of contacts infected and risk ratios (RRs) were used to quantify the strength of this association.

Results: There were 4190 (2312 pulmonary and 1878 extrapulmonary) index TB patients and 18,030 contacts. A total of 15,522 contacts were tested with TST, of whom 3213 had a result of 10mm. The dispersion parameter, k for secondary infections was estimated at 0.16 (95%CI 0.14-0.17) and there were 414 (9.9%) super-spreading events. From the 3213 secondary infections, 2415 (75.2%) were due to super-spreading events. There were 226 contacts who developed active TB disease and a higher level of heterogeneity was found for this outcome than for secondary infection, with k estimated at 0.036 (95%CI 0.025-0.046). In regression analyses, we found that infectiousness was greater among index patients found by clinical presentation and those with bacteriological confirmation.

Conclusion: TB transmission is highly over dispersed and super-spreading events are responsible for a substantial majority of secondary infections. Heterogeneity of transmission and super-spreading are critical issues to consider in the design of interventions and models of TB transmission dynamics.

Item ID: 57814
Item Type: Article (Research - C1)
ISSN: 1471-2334
Keywords: Tuberculosis, Super-spreading, Negative binomial distribution, Victoria
Copyright Information: © The Author(s). 2019 Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver( applies to the data made available in this article, unless otherwise stated.
Funders: Monash University (MU), National Health and Medical Research Council (NHMRC)
Projects and Grants: MU Monash Graduate Scholarship, NHMRC Early Career Fellowship
Date Deposited: 03 Apr 2019 07:48
FoR Codes: 32 BIOMEDICAL AND CLINICAL SCIENCES > 3202 Clinical sciences > 320211 Infectious diseases @ 50%
42 HEALTH SCIENCES > 4202 Epidemiology > 420202 Disease surveillance @ 50%
SEO Codes: 92 HEALTH > 9201 Clinical Health (Organs, Diseases and Abnormal Conditions) > 920109 Infectious Diseases @ 50%
92 HEALTH > 9204 Public Health (excl. Specific Population Health) > 920404 Disease Distribution and Transmission (incl. Surveillance and Response) @ 50%
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