NSW authorities are urging people to be alert to meningococcal disease symptoms as a peak nears, saying the potentially-deadly infection is hard to identify.

Health authorities are urging NSW residents to be alert to meningococcal disease symptoms as the peak infection period approaches, after the death of a toddler, one of 21 recorded cases this year.

Vicky Sheppeard from NSW Health says cases normally rise towards the end of flu season, when people's immune systems are weaker from viruses.

"Meningococcal disease is a rare but serious bacterial infection that can cause death within hours and it's hard to identify, so the more symptoms people know about, the better," Dr Sheppeard, the director of communicable diseases, said in a statement on Thursday.

"Often it can mimic other common illnesses, so be aware nearer spring that nausea symptoms, vomiting, neck stiffness, joint pain, light sensitivity, or a sudden fever, could be something else."

The warning comes after the Hunter New England Local Health District confirmed earlier this week that a toddler had died from the infection in the fourth case of meningococcal disease in the region this year.

Dr Sheppeard said people normally associated the disease with a rash of red-purple spots or bruises, but a rash didn't always appear and could be the last symptom.

Vaccination is available for meningococcal disease types A, C, W and Y, however, there are other strains so vaccinated people should still look out for symptoms.