Eighteen linked pairs give a mean serial interval of 24.2 days in PU650's Unit 2 transmission analysis, four days shorter than hepatitis A's usual incubation. Searches like "pu 650 unit 2 assignment example", "pu650 unit 2 sample" and "pu650 unit 2 example" land here.
What a finished PU650 Unit 2 transmission analysis looks like
The analysis opens with a table of the eighteen pairs: infector onset date, infectee onset date, the interval in days and the tracing evidence that linked them, such as a shared tent or shared drug equipment. Intervals run from 16 to 33 days. Beneath the table sits the script's output: mean 24.2 days, standard deviation 4.6, and a growth rate of 0.22 per week fitted to ten weeks of counts. Converted with the serial interval, that growth implies a reproduction number near 2.1, close to the 2.2 given by counting secondary cases around nine early index cases. A route section follows, then a paragraph on why an interval shorter than the incubation period points to transmission before symptoms. The whole script, about twenty lines of Python, is appended so a grader can rerun it.
How a PU650 Unit 2 example is structured
Timing comes before mechanism because a transmission prompt asks how the virus moves, and the pairs answer that more directly than any textbook description. The serial interval is computed first, since both reproduction estimates depend on it. Two estimates follow, one from the epidemic's growth and one from counted offspring, and the analysis treats their agreement as the main evidence that either is sound. Route comes next: fecal-oral spread through hands, shared food and drug equipment in places with few toilets or sinks. A closing section reads the gap between serial interval and incubation, about four days, as evidence that people passed the virus on before they felt ill, which explains why isolating people once jaundiced came too late to break chains. Each figure is labeled an effective reproduction number, not R0, because some residents were already immune.
Eighteen pairs in one table
Each row gives both onset dates, the interval and the tracing link, whether a shared tent, a shared meal line or shared needles. Two pairs with doubtful direction are kept but flagged, and the script is run with and without them.
Growth rate to reproduction number
Ten weekly counts, rising from 3 to 21, are fitted on the log scale for a growth rate of 0.22 per week. A gamma-shaped interval with the observed mean and spread converts that growth to about 2.1.
A second estimate from offspring
Nine index cases traced early produced twenty secondary cases between them, an average of 2.2. Tracing misses some secondary cases in a mobile population, the analysis notes, so this figure is more likely low than high.
Route and setting
Fecal-oral transmission needs hands and mouths to meet contaminated surfaces, and encampments without toilets or sinks supply that daily. Shared drug equipment and shared food add routes that shelter crowding alone would not explain.
What the four-day gap changes
Because shedding peaks before symptoms, isolation triggered by jaundice arrives after most transmission has happened. The section closes on vaccinating contacts within two weeks of exposure and on sanitation, the two controls this route supports.
Where marks go in PU650 Unit 2
Transmission rubrics in PU650 generally split credit between the calculation, the reasoning built on it and the controls that follow, and the example is weighted to match. A serial interval reported without its pairs cannot be checked, so the table and the script are both on the page. The four-day gap earns the reasoning marks, since it turns a number into a claim about when people are infectious. Control credit requires that every measure answer the route. Typical losses here: a reproduction number quoted from a textbook instead of computed from the data supplied, R0 and the effective figure used interchangeably, an interval computed from report dates rather than onset dates, and controls such as masks recommended for a virus that does not travel through the air.
Get a PU650 Unit 2 example written to your instructions
Name the pathogen the PU650 Unit 2 prompt assigns and say whether it supplies case pairs, weekly counts or neither. Those two facts, plus the instructions and rubric, let a free first custom sample come back in 24-48 hours: route, serial interval and reproduction number worked from those data, with the script behind each figure attached.
PU650 Unit 2 questions, answered
What if the PU650 Unit 2 prompt gives no line list?
Then the analysis works from published parameters, cited with their setting and year, and says plainly that nothing was computed from local data. For hepatitis A, the CDC's incubation range of 15 to 50 days with an average near 28 is the usual anchor. A reproduction number borrowed that way is described as someone else's estimate, never presented as a finding.
Why compute the reproduction number two ways?
Each method fails differently. The growth-rate route depends on the assumed shape of the interval and on steady reporting, while the offspring count depends on how completely contact tracing found secondary cases. When the two land close together, as 2.1 and 2.2 do here, a grader has reason to trust both. When they diverge, the analysis explains which assumption probably broke.
Is the Pellham outbreak based on a real one?
It is composite, though its shape resembles person-to-person hepatitis A outbreaks among people experiencing homelessness in several US cities after 2016. San Diego's, which the county reported at close to 600 cases and 20 deaths, is the one most often cited. The example names that event only as context and draws none of its figures from it.