The group urged countries approaching their summer seasons to prepare their health systems for a rise in dengue cases.
As Bangladesh's dengue outbreak spreads outside the capital, Nigeria battles another diphtheria wave and Uruguay reports its first H5 detection in a sea lion.
With a new case in Miami-Dade County, Florida now has 16 dengue infections for the year.
New York City dermatologists have noted severe fungal infections, and Argentina reports H5 avian flu in sea lions.
The WHO guidance replaces temporary recommendations, Florida has 15 dengue cases now, and Connecticut confirms 4 people infected with the tick-borne Powassan virus.
County officials have issued a mosquito-borne illness alert following the detection of 2 local dengue cases.
Bangladesh is experiencing an unusual surge in activity that started earlier than usual and has a relatively high case-fatality rate.
Several of the El Nino health risks are due to water contamination, either from flooding or drought. Malnutrition due to food insecurity was the top threat.
The WHO said more investigations are needed to the rise in GBS cases, though some patients tested positive for Campylobacter infection.
E-11 viruses isolated from some of Italy's cases belong to the same genetic cluster as those isolated from France.