Mean, upper 90% Confidence Interval and 95th percentiles for six surveillance datasets.

<p>Mean, upper 90% Confidence Interval and 95th percentiles for six surveillance datasets.</p

Categories of influenza season in Victoria for six surveillance datasets, 2002-2011.

<p>Categories of influenza season in Victoria for six surveillance datasets, 2002-2011.</p

WHO method for determining thresholds.

<p>Figure adapted from the WHO Global Surveillance Standards for Influenza [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077244#B7" target="_blank">7</a>].</p

Average incubation period in combined cohorts (n = 43) according to variables investigated.

<p>Average incubation period in combined cohorts (n = 43) according to variables investigated.</p

The incubation period of Buruli ulcer (<i>Mycobacterium ulcerans</i> infection) in Victoria, Australia – Remains similar despite changing geographic distribution of disease

<div><p>Background</p><p>Buruli ulcer (BU) is a geographically-restricted infection caused by <i>Mycobacterium ulcerans</i>; contact with an endemic region is the primary risk factor for disease acquisition. Globally, efforts to estimate the incubation period of BU are often hindered as most patients reside permanently in endemic areas. However, in the south-eastern Australian state of Victoria, a significant proportion of people who acquire BU are visitors to endemic regions. During a sustained outbreak of BU on the Bellarine peninsula we estimated a mean incubation period of 4.5 months. Since then cases on the Bellarine peninsula have declined but a new endemic area has developed centred on the Mornington peninsula.</p><p>Method</p><p>Retrospective review of 443 cases of BU notified in Victoria between 2013 and 2016. Telephone interviews were performed to identify all cases with a single visit to an endemic region, or multiple visits within a one month period. The incubation period was defined as the time between exposure to an endemic region and symptom onset. Data were subsequently combined with those from our earlier study incorporating cases from 2002 to 2012.</p><p>Results</p><p>Among the 20 new cases identified in short-term visitors, the mean incubation period was 143 days (4.8 months), very similar to the previous estimate of 135 days (4.5 months). This was despite the predominant exposure location shifting from the Bellarine peninsula to the Mornington peninsula. We found no association between incubation period and age, sex, location of exposure, duration of exposure to an endemic region or location of BU lesion.</p><p>Conclusions</p><p>Our study confirms the mean incubation period of BU in Victoria to be between 4 and 5 months. This knowledge can guide clinicians and suggests that the mode of transmission of BU is similar in different geographic regions in Victoria.</p></div

Incubation period ranges and midpoints for 20 patients in current study cohort.

<p>Incubation period ranges and midpoints for 20 patients in current study cohort.</p

Characteristics of 43 cases from Trubiano et al. [15] and current study cohorts.

<p>Characteristics of 43 cases from Trubiano et al. [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0006323#pntd.0006323.ref015" target="_blank">15</a>] and current study cohorts.</p

Regions near Melbourne considered endemic for <i>Mycobacterium ulcerans</i>.

<p>Image with adapted text from Trubiano et al. [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0006323#pntd.0006323.ref015" target="_blank">15</a>] as per the Creative Commons Attribution license. Small endemic region of East Gippsland not shown, 250km east of Melbourne.</p

Number and percentages of BU lesions stratified by gender, age, exposure location and body regions.

<p>Number and percentages of BU lesions stratified by gender, age, exposure location and body regions.</p

Density maps stratified by gender.

<p>Density maps stratified by gender.</p