Timeliness and impact of public health responses to measles outbreaks in the United States 2001-2017 Open Access
Mahood, Duncan (Spring 2019)
Abstract
We assessed the timeliness of public health response to measles cases and outbreaks in the United States from 2001-2017 and quantified reductions in transmissibility (measured by the case reproduction number, Rc, or average number of secondary cases generated per case) following initiation of public health responses. Incidence time-series and the distribution of the serial interval (time between symptom onset of primary case to symptom onset of secondary attributable case) were used to quantify the Rc. The median number of days from rash onset to health department notification or case investigation was 2 days (sd: 10.66) and 5 days (sd: 10.50) respectively, while the median earliest date of public health response (either notification or investigation) to outbreaks was 8 days (sd: 8.68). For each daily increase in delay of public health response, case reproduction number went up an average of 0.038 (95% CI: 0.028, 0.047) for unvaccinated cases, 0.015 (95% CI: 0.01, 0.02) for vaccinated cases, and 0.020 (95% CI: 0.012, 0.028) for cases with unknown vaccination status. During the period of infectivity, the difference between response on the first day of infectivity (4 days before rash onset) and the last day of infectivity equates to 0.45 (0.41 to 0.85) additional transmissions per case. During outbreaks, Rc on or before and after index case response date was 1.47 and 0.15, respectively; absolute difference of 1.31, 95% CI (1.16, 1.46) additional infections per case. Overall, Rc for cases that were responded to before or during and after their period of infectivity was 0.60 and 0.84, respectively; absolute difference of 0.24 (95% CI: 0.10, 0.38) additional infections per case. These findings support the hypothesis that public health response reduces the probability of per-case transmission for (1) individual cases and (2) outbreaks overall, and that these trends are 2.5 times stronger for unvaccinated cases compared to vaccinated cases. To minimize local transmission, public health response should aim to investigate cases as soon as possible during the period of infectivity.
Table of Contents
BACKGROUND .......................................................................................................1
METHODS...............................................................................................................2
SUMMARY ANALYSIS..........................................................................................2
RELATIONSHIP BETWEEN RESPONSE TIME AND RC .......................................3
IMPACT OF PUBLIC HEALTH RESPONSE: RC ESTIMATION ..............................5
RESULTS .................................................................................................................5
SUMMARY ANALYSIS..........................................................................................5
PUBLIC HEALTH RESPONSE TIME......................................................................5
RELATIONSHIP BETWEEN CASE RESPONSE TIME AND RC ..............................7
IMPACT OF PUBLIC HEALTH RESPONSE TO OUTBREAKS ................................8
DISCUSSION............................................................................................................8
PUBLIC HEALTH RESPONSE TIME......................................................................9
RELATIONSHIP BETWEEN CASE RESPONSE TIME AND RC ............................10
IMPACT OF PUBLIC HEALTH RESPONSE TO OUTBREAKS ...............................11
LIMITATIONS .....................................................................................................12
IMPLICATIONS ......................................................................................................12
REFERENCES .........................................................................................................14
TABLES & FIGURES............................................................................................... 16
FIGURE 1.............................................................................................................16
TABLE 1 ..............................................................................................................17
FIGURE 2.............................................................................................................18
FIGURE 3.............................................................................................................19
FIGURE 4.............................................................................................................20
FIGURE 5A ..........................................................................................................21
FIGURE 5B ..........................................................................................................22
FIGURE 5C ..........................................................................................................23
FIGURE 6A ..........................................................................................................24
FIGURE 6B ..........................................................................................................25
FIGURE 6C ..........................................................................................................26
About this Master's Thesis
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Timeliness and impact of public health responses to measles outbreaks in the United States 2001-2017 () | 2019-04-22 21:34:07 -0400 |
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