Paediatric infectious diseases are communicable diseases that affect children. If a child develops persistent illness as a result of an infectious agent, an infectious diseases specialist has the experience and training to properly diagnose and treat the child from infancy through adolescence. The impact of developmental changes that occur during the birth period, infancy, childhood, and adolescence will lead to more rational, safer, and effective drug usage in the paediatric population. Infectious and immunologic disorders caused by bacteria, viruses, fungi, and parasites are treated by paediatric infectious diseases experts. For more complex infections, other paediatric infectious diseases specialists are consulted.