The time that it takes for the symptoms of listeriosis to develop after an initial listeria infection (the incubation period) can vary considerably from one to 90 days. The average incubation time is around 30 days.
Most cases of listeria infection are limited to the digestive system (non-invasive listeriosis). The symptoms include:
- a high temperature (fever) of 38ºC (100.4ºF) or above
- muscle pain
- chills
- feeling sick
- being sick
- diarrhoea
Invasive listeriosis
When the infection spreads into the blood (septicaemia) or the central nervous system (invasive listeriosis), the symptoms of fever, muscle pain and chills tend to be much more severe.
If the infection spreads to the nervous system and the brain, additional symptoms can include:
- severe headache
- stiff neck
- changes in mental state, such as confusion
- seizures (fits)
- lack of physical co-ordination
- uncontrollable shaking or twitching (tremor)
If listeriosis spreads to the brain, it can cause meningitis. This is an infection of the membranes that surround the brain and spinal cord.
See the Health A-Z topic about Meningitis for more information.
Listeriosis in babies
Symptoms of listeriosis in babies can include:
- lack of interest in feeding
- irritability
- seizures
- breathing difficulties, such as rapid breathing or grunting when breathing
- skin rash
- a higher or lower temperature than normal
The normal body temperature for a baby is around 37ºC (98.6ºF). For more information, see what is a high temperature in children?
