Peridomestic Infection as a Determining Factor of Dengue Transmission

Abstract

Background: The study of endemic dengue transmission is essential for proposing alternatives to impact its burden. The traditional paradigm establishes that transmission starts around cases, but there are few studies that determine the risk.

Methods: To assess the association between the peridomestic dengue infection and the exposure to a dengue index case (IC), a cohort was carried out in two Mexican endemic communities. People cohabitating with IC or living within a 50-meter radius (exposed cohort) and subjects of areas with no ICs in a 200-meter radius (unexposed cohort) were included.

Results: Exposure was associated with DENV infection in cohabitants (PRa 3.55; 95%CI 2.37-5.31) or neighbors (PRa 1.82; 95%CI 1.29-2.58). Age, location, toilets with no direct water discharge, families with children younger than 5 and the House Index, were associated with infection. Families with older than 13 were associated with a decreased frequency. After a month since the IC fever onset, the infection incidence was not influenced by exposure to an IC or vector density; it was influenced by the local seasonal behavior of dengue and the age. Additionally, we found asymptomatic infections accounted for 60% and a greater age was a protective factor for the presence of symptoms (RR 0.98; 95%CI 0.97-0.99).

Conclusion: The evidence suggests that dengue endemic transmission in these locations is initially peridomestic, around an infected subject who may be asymptomatic due to demographic structure and endemicity, and it is influenced by other characteristics of the individual, the neighborhood and the location. Once the transmission chain has been established, dengue spreads in the community probably by the adults who, despite being the group with lower infection frequency, mostly suffer asymptomatic infections and have higher mobility. This scenario complicates the opportunity and the effectiveness of control programs and highlights the need to apply multiple measures for dengue control.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Accumulated Distribution of Groups in Axochiapan (A) and Tepalcingo (B).

IC houses in red, IC neighbor houses in blue (exposed group) and unexposed group houses in green. Areas have 50, 100 and 200 meters in diameter with the center at the IC house or in the centroid of unexposed the neighbor houses. Source: Esri, DigitalGlobe, GeoEye, i-cubed, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community.

Fig 2. Cohort Enrollment and Follow-up.

*Two 3-year-old children were included because they had pre-enrollment symptomatic infections diagnosed by the SSM.

Fig 3. Pre-enrollment DENV Infections per Age.

A. Pre-enrollment infection cases (n = 213/1,172), B. Frequency of pre-enrollment infections.

Fig 4. Post-enrollment DENV Infections per Age.

A. Post-enrollment infection cases (n = 40/922), B. Frequency of post-enrollment infections.

Fig 5. Proposed Dengue Transmission in Studied Communities.

Force of infection (λ). Symptomatic (Sx). Asymptomatic (Asx). Index Case (IC). Infection (Inf). Years old (y/o). Destination, includes workplace and other locations where subjects spend enough time to be bitten by vectors located in that area; except for schools.