What are the symptoms of infectious diseases?

Key facts

  • Infectious diseases can cause severe illness in adolescents. Even if treated, some of these diseases can have life-long effects on the adolescents who catch them.

  • It is useful for all parents to know how to recognise the early signs of these diseases, so they can get help for their adolescent if needed.

  • If you decide not to vaccinate your adolescent, they will be at an increased risk of catching an infectious disease and of getting seriously ill.

Last updated on 13 August 2025.

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Introduction

It is useful for parents to know how to recognise early signs of serious infectious diseases in their adolescent, so they can get help if needed.

The risks associated with serious infectious diseases are higher for adolescents who have not been vaccinated or have not had all of their vaccinations on time than for those who are fully vaccinated. This includes the risk of the adolescent catching an infection, and the risk of an infection developing into serious illness. Even with treatment, some of these diseases can have life-long effects on the adolescents who catch them.

Symptoms to watch out for

Many serious infectious diseases in adolescents start out looking like a common cold. This means it can be difficult to tell when it is something more serious. Below is a list of symptoms that could be a sign of serious disease.

It is important to note that not all adolescents who are seriously ill have one of the symptoms listed below. If your adolescent seems unusually sick, you should:

  • call an ambulance on 000
  • go to your local emergency department or see your doctor as soon as you can
  • call Healthdirect on 1800 022 222.

Fever is a sign of many infectious diseases. The symptoms of fever can vary. A person may have a fever if they have a high body temperature, if their skin is hot to the touch or if they are shivering even though they are warmly dressed. Fever can also make adolescents sleepy, drowsy, move slower than normal (lethargic) or make their skin look pale or mottled.

You should take your adolescent to hospital immediately if they have a fever and at the same time:

  • light seems to hurt their eyes
  • they have a stiff neck
  • they have a rash that does not fade when you press on it with a drinking glass (for more information, see ‘Rash’ below).

If you need an ambulance to take you and your adolescent to a hospital, call 000.

If your adolescent has a fit (seizure) and they have never had one before, it could be a sign they have meningitis (a brain infection). Meningitis can be caused by viruses (e.g. influenza) or bacteria (e.g. meningococcal and pneumococcal disease). In this situation, call an ambulance on 000.

Sometimes adolescents who have serious lung infections (like pneumonia) have long coughing fits. These fits can make it hard for them to breathe. If your adolescent has a cough that gets persistently worse over a few days, see a doctor. If they have any difficulty breathing, call an ambulance on 000. These symptoms might be caused by whooping cough (pertussis) or pneumococcal disease.

Sometimes adolescents who are seriously ill will get blue lips due to low oxygen levels, either with or without a coughing fit. These are symptoms of possible lung infections (like pneumonia) caused by whooping cough (pertussis) or pneumococcal disease.

If your adolescent develops a rash, test to see if it fades (or ‘blanches’) when you push on it. Some parents do this by pushing the skin with a finger for a few seconds, then letting go. Others push a clear drinking glass onto the skin, bottom side down, and then look to see if the rash fades underneath the bottom of the glass. A rash that doesn’t fade could be caused by meningococcal disease. Usually, the rash does not appear until the adolescent is very sick. If your adolescent has a rash like this, call an ambulance on 000.

Rashes that start when, or soon after, an adolescent gets a fever, runny nose, sore throat, swollen or tender neck, or headache are a sign of many serious infectious diseases.

If your adolescent has an injury that causes a break in the skin, dirt can get into the wound. If that dirt contains tetanus spores, they can get a tetanus infection. Animal bites, scratches from thorns or sharp stones in the garden, and punctures from old nails can all cause a tetanus infection. Wounds can become infected very quickly, so it is important to see a doctor straight away if your adolescent gets an injury like this.

For more information, see this guideline on when to seek medical advice for tetanus prone wounds from the Royal Children’s Hospital Melbourne.

Certain types of human papillomavirus (HPV) can cause genital warts. These look like small lumps that can be found around the vagina, penis or anus. HPV can also cause benign (non-cancerous) tumours that grow in the throat (recurrent respiratory papillomatosis).1

For more information about the symptoms of infectious diseases, access this Healthdirect webpage.

What should I do if there is an outbreak of disease?

If you are aware of an outbreak of disease where you live and you want to protect your adolescent from getting sick, get in touch with your doctor, nurse or community healthcare provider. It is never too late to vaccinate. Some parents reconsider vaccinating their adolescents if there is an outbreak of a disease in their community.

What should I do if I think my adolescent has an infectious disease?

If your adolescent is sick and you suspect they have an infectious disease, contact your doctor, nurse or community healthcare provider. It is important to call before you visit so they can make sure there is no one in the waiting room who could get very ill if they catch a vaccine preventable disease, such as people with certain illnesses or people who are having certain medical treatments such as chemotherapy.

Medicines like antibiotics, antivirals and immunoglobulins (also known as antibodies) are available to treat some infectious diseases. Treatment depends on your adolescent’s vaccination status and underlying health conditions. It is usually best to start taking these medicines as soon as possible.

Please note: In SKAI Adolescent, the phrase ‘your adolescent’ refers to all guardian relationships where health decisions for an adolescent fall under your responsibility.

Drafts of this page were reviewed by members of our Consumer Advisory Group


  1. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Human Papillomaviruses. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. 2007;90. Available from https://publications.iarc.fr/108