Background
The authors write that "the mosquito-borne dengue viruses are a major public health problem throughout the tropical and subtropical regions of the world," and that "changes in temperature and precipitation have well-defined roles in the transmission cycle and may thus play a role in changing incidence levels." Therefore, as they continue, since "the El Niņo Southern Oscillation (ENSO) is a multiyear climate driver of local temperature and precipitation world wide," and since "previous studies have reported varying degrees of association between ENSO and dengue incidence," as they describe it, they decided to analyze "the relationship between ENSO, local weather, and dengue incidence in Puerto Rico, Mexico, and Thailand.

What was done
Johansson et al. searched for relationships between ENSO, local weather and dengue incidence in Puerto Rico (1986-2006), Mexico (1985-2006), and Thailand (1983-2006) using wavelet analysis as a tool to identify time- and frequency-specific associations.

What was learned
The three researchers report that they "did not find evidence of a strong, consistent relationship in any of the study areas," while Rohani (2009), who wrote a Perspective piece on their study, states that the three researchers found "no systematic association between multi-annual dengue outbreaks and El Niņo Southern Oscillation." Thus, as stated in the "Editors' Summary" of Johansson et al.'s paper, their findings "provide little evidence for any relationship between ENSO, climate, and dengue incidence."

What it means
In light of the inconclusive nature of Johansson et al.'s analysis, there still remains a lack of substantive real-world support for the climate-alarmist claim that global warming promotes the global intensification and spread of the spectrum of diseases caused by the different serotypes of the family of dengue viruses.

Reference
Rohani, P. 2009. The link between dengue incidence and El Niņo Southern Oscillation. PLoS Medicine 6: e1000185.