Research ArticleHEALTH AND MEDICINE

Combining contact tracing with targeted indoor residual spraying significantly reduces dengue transmission

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Science Advances  17 Feb 2017:
Vol. 3, no. 2, e1602024
DOI: 10.1126/sciadv.1602024
  • Fig. 1 Metropolitan DENV epidemic transmission evidenced through contact tracing.

    (A) Total of 902 confirmed DENV cases during the 2008–2009 outbreak and associated exposure locations reported through contact tracing. Blue dots show the contact locations of the epidemic’s index case, which initiated outbreaks both in Cairns and Clifton Beach. (B) Relative connectivity between towns, measured as the proportion of all contact locations of DENV cases residing in a given town that occurred at the other towns and thickness proportional to relative frequency of total locations (range, 0.1 to 1). For instance, an arrow going from Palm Cove (north) to Cairns shows that 50% of all contact locations occurred in Cairns (and the remaining 50% locations in Palm Cove, as no other lines connect Palm Cove to other towns). Location of towns in the network is proportional to their geographic location. (C) Probability density distribution (Pb) showing that a confirmed DENV case moved a given distance from his or her residence (Δd), calculated both for Cairns and satellite town residents. (D) Same as (C), showing detail for the distance range of 0 to 500 m. (E) Proportion of all contact locations of a given town that were found in the city of Cairns as a function of the Euclidian distance of each town to Cairns. The linear relationship was statistically significant (P = 0.03).

  • Fig. 2 Sources and sinks of metropolitan DENV transmission.

    Space-time interaction tests identified putative virus transmission sites for 823 of 902 symptomatic laboratory-confirmed DENV cases during the 2008–2009 outbreak. The resulting DENV transmission network shows Cairns as the primary virus transmission hub. Direction of arrows indicates residents of a locality (origin) whose exposure occurred on a different locality (destination) and the thickness of edges is proportional to the total number of locations that occurred on a given destination locality. Numbers inside each pink circle point to the proportion of putative transmission locations that occurred within that locality. For instance, for residents of Palm Cove (north), none of the contact locations in the town were associated with local DENV transmission. Instead, all transmission locations of Palm Cove residents occurred within Cairns.

  • Fig. 3 Spatiotemporal pattern of DENV propagation within Cairns.

    Locations that were statistically linked in space-time and where DENV transmission was likely to occur (that is, putative transmission locations). Colors show the week of onset of symptoms (measured as time since the onset of symptoms of the epidemic’s index case). Panels on the right show the same data but in temporal cuts as the epidemic progressed.

  • Fig. 4 Location types involved in DENV transmission chains.

    Proportion of participants whose putative transmission locations identified by space-time interaction tests included their home only, one or more out-of-home locations, or both the home and out-of-home locations.

  • Fig. 5 Impact of TIRS performed on contact locations on the occurrence of future dengue cases.

    Expressed as the proportion of locations with DENV cases at a given time after intervention (treatment locations; dashed line) or onset of symptoms of the first DENV case (control locations; solid line).

  • Table 1 Effectiveness of TIRS applied at contact locations in preventing dengue symptomatic infections during the 2008–2009 DENV outbreak that occurred in Cairns, Australia.
    ScenarioTreatmentTotal locationsNo. of DENV-positive locationsProportion infectionEffectiveness
    All casesIRS1007520.0520.861
    Control3691370.371
    Excluding first 10 days*IRS817110.0130.961
    Control3251130.348

    *This scenario excludes the first 10 days after intervention to exclude transmission events likely originated before the intervention.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/2/e1602024/DC1

      Supplementary Text

      fig. S1. Distribution of contact locations (including the home residence) reported by each confirmed case of DENV.

      fig. S2. Results from local space-time interaction test, showing the contact locations and significant space-time links found within prespecified windows of 100 m and 20 days.

      fig. S3. DENV transmission chains.

      fig. S4. The cumulative number of confirmed symptomatic cases of DENV reported (blue) and the cumulative number of targeted indoor residual sprays performed (orange) during the 2008–2009 outbreak that affected the metropolitan Cairns area, Australia.

      fig. S5. Distribution of interventions performed in Cairns in response to the 2009 DENV-3 epidemic: TIRS with pyrethroid insecticides, the placement of lethal A. aegypti ovitraps, and community education (State Emergency Service).

      fig. S6. Temporal distribution of the number of locations analyzed in the Cox proportional hazards model evaluating the impact of TIRS on dengue transmission.

      fig. S7. Spatial distribution of locations analyzed in the Cox proportional hazards model evaluating the impact of TIRS on dengue transmission.

      fig. S8. Number of secondary dengue cases spatiotemporally linked to locations TIRS-sprayed or not sprayed at all (control).

      fig. S9. Form used by Queensland’s medical general practitioners reporting suspected or confirmed cases to the Tropical Public Health Unit.

      fig. S10. Dengue case report forms used by the Tropical Public Health Unit nurses to interview suspected or confirmed dengue cases (and their contacts) and ascertain the locations visited while viremic and, ultimately, the most likely place of transmission (called “acquired where” in the form).

    • Supplementary Materials

      This PDF file includes:

      • Supplementary Text
      • fig. S1. Distribution of contact locations (including the home residence) reported by each confirmed case of DENV.
      • fig. S2. Results from local space-time interaction test, showing the contact locations and significant space-time links found within prespecified windows of 100 m and 20 days.
      • fig. S3. DENV transmission chains.
      • fig. S4. The cumulative number of confirmed symptomatic cases of DENV reported (blue) and the cumulative number of targeted indoor residual sprays performed (orange) during the 2008–2009 outbreak that affected the metropolitan Cairns area, Australia.
      • fig. S5. Distribution of interventions performed in Cairns in response to the 2009 DENV-3 epidemic: TIRS with pyrethroid insecticides, the placement of lethal A. aegypti ovitraps, and community education (State Emergency Service).
      • fig. S6. Temporal distribution of the number of locations analyzed in the Cox proportional hazards model evaluating the impact of TIRS on dengue transmission.
      • fig. S7. Spatial distribution of locations analyzed in the Cox proportional hazards model evaluating the impact of TIRS on dengue transmission.
      • fig. S8. Number of secondary dengue cases spatiotemporally linked to locations TIRS-sprayed or not sprayed at all (control).
      • fig. S9. Form used by Queensland’s medical general practitioners reporting suspected or confirmed cases to the Tropical Public Health Unit.
      • fig. S10. Dengue case report forms used by the Tropical Public Health Unit nurses to interview suspected or confirmed dengue cases (and their contacts) and ascertain the locations visited while viremic and, ultimately, the most likely place of transmission (called “acquired where” in the form).

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