These can be either new infections, like COVID-19 was in 2020, or a known infection that is spreading rapidly, such as measles today.
- Emerging infections are new diseases that have recently appeared in a population; known diseases that have spread to new areas or populations; known diseases that are spreading more quickly; or known diseases that do not respond to standard treatments. Examples include COVID-19, mpox and Zika.
- Reemerging infections are known diseases that have come back after being mostly controlled, or known diseases that are reappearing due to new strains or breakdowns in public health measures. Examples include measles, pertussis and malaria.
- Drug-resistant infections are infections caused by pathogens that have become resistant to antimicrobial drugs, such as antibiotics, antivirals or antifungals. This makes infections harder to treat, resulting in longer hospital stays and, in some cases, death. Examples include the fungus Candida auris and methicillin-resistant Staphylococcus aureus, a drug-resistant bacterium.

