What's the Difference Between Infectious and Contagious?

Have you ever wondered if infectious means the same thing as contagious? If so, and you still don't know the answer, you can read this article. We'll tell you the difference here.

Reviewed and approved by the nurse Leidy Mora Molina.

Written by Rafael Victorino Muñoz

Last update: 01 December, 2022

Although one or the other term is sometimes used interchangeably in everyday language, there are some crucial differences between the terms infectious and contagious. However, both terms also have their similarities, since both types refer to infections that are caused by pathogens.

Contagious diseases are, in fact, considered to be infectious, but not all infectious diseases are contagious. The major difference between them has to do with transmission from person-to-person contact. We’ll take a look at this in more detail below.

Infectious diseases

According to a variety of factors, such as the organs affected, the time at which they appear, and other criteria, there are different types of diseases: autoimmune, neurological, endocrine, skin, blood, pregnancy, degenerative, and neoplasms, among others.

In particular, we speak of infectious diseases to refer to those that are caused by a pathogen that enters the body, triggering a series of reactions. This process is what is known as an infection.

Types of infections

In turn, there can be of various kinds of infections depending on the pathogenic microorganisms or germs that produce them; in this sense, they can be categorized into the following groups

• Bacterial infections: These are caused, as the name implies, by bacteria; some examples of this type of diseases are streptococcal pharyngitis (group A β-hemolytic streptococcus β-hemolytic streptococcus); gastroenteritis (Campylobacter jejuni, E Coli, Salmonella, Shigella or Staphylococcus, among others);  pneumonia (Haemophilus influenzae type b (Hib), and Streptococcus pneumoniae); and otitis (Haemophilus influenzae (non-typeable) and Streptococcus pneumoniae).
• Viral diseases: These are caused by viruses such as HIV, HPV, herpes, influenza, mononucleosis, and conjunctivitis.
• Mycoses: These are caused by fungi, such as Tinea pedis (athlete’s foot), candidiasis, and aspergillosis.
• Parasitic diseases: There are vaccines for infectious and contagious parasitic diseases, such as chicken pox, toxoplasmosis, Chagas disease, leishmaniasis, malaria, pinworms, and others.

Form of transmission

Now, pathogens can enter the body in various ways. Among these, it’s worth distinguishing a few of the most common entryways:

• Through the bite of an insect or other animal, called an “agent” (this is the case of dengue fever, for instance).
• Consumption of contaminated water or food, as in the case of gastroenteritis.
• An open wound can be a gateway for bacterial skin infections.
• Contact with a sick person; this is the case of contagious diseases we will see below.

Contagious diseases

As has been seen, contagious diseases are a class within infectious diseases. In fact, it could be said that this constitutes a first, albeit partial, difference between them.

Likewise, in the previous section it was also mentioned that in the case of contagious diseases, transmission occurs directly between individuals by contact between a sick person and a healthy one.

The similarity between the words contact and contagion, in this context, speaks for itself. However, there’s still an additional distinction to be made with regard to the transmission of these diseases.

Direct contagion is said to occur when people come into contact with each other; this can occur through secretions (coughing or sneezing), if there’s an exchange of fluids (saliva or others), or by touching open wounds; etc.

Indirect contagion occurs when someone uses an object belonging to the sick person; for example, athlete’s foot can be transmitted by sharing shoes or other items of clothing. Some examples of contagious diseases, in addition to those mentioned above, are cases of the flu and colds, HPV, herpes, and hepatitis A, among others.

The similarities and differences between infectious and contagious

Next, we will delve into the similarities and differences between infectious and contagious in relation to various aspects, such as treatment, symptoms, and other things.

Causative agents

The same types of agents that we have already seen can produce various infectious or contagious diseases indistinctly. In this sense, there are no major differences between the two.

In other words, there may be bacterial, fungal, viral, or parasitic contagions that are transmitted from one person to another. However, food poisoning can only be infectious.

This is the case of diseases such as cholera, which is caused by the bacterium Vibrio cholerae. The main route of transmission is through the consumption of contaminated water or food, and direct transmission from one individual to another is uncommon.

2. Symptoms

The signs of infectious and contagious diseases can also be similar. Within them, there are some nonspecific or general symptoms, and others more particular.

For example, in the case of diseases caused by viruses or bacteria, fevers and general malaise are often manifested. This is observed equally in viral gastroenteritis and in tonsillitis, the latter being contagious, but not the former.

3. Treatment

As with symptoms, there are usually not many differences between infectious and contagious as far as treatment is concerned. In some cases, antibiotics, antivirals, or antifungals are applied, if they are of bacterial, viral, or fungal origin, respectively. Other medications, such as analgesics, are also administered.

4. Prevention

It is on the subject of prevention that we will see the biggest differences between infectious and contagious diseases. Although some care measures, such as hand washing, may be common to both, there are some that are particular to each of these categories.

For example, washing food, cooking it well before eating, avoiding eating food in the street, and consuming only distilled water, among others, are measures to avoid certain infections of the digestive tract. On the other hand, since transmission in the case of contagious diseases is from individual to individual, measures include:

• In the case of sick persons, cover with a handkerchief when coughing or sneezing.
• Healthy people should avoid or reduce direct contact with sick people.
• Wear gloves and masks if you are going to be with sick people.
• Do not share utensils, clothing, or footwear with sick people.
• Disinfect utensils, as well as common spaces and elements exposed to fluids and secretions (fomites): tables, chairs, and doors.
• Use condoms to prevent the spread of sexually transmitted diseases.
• Finally, there are vaccines for infectious and contagious diseases, such as chickenpox.

5. Public health

Finally, in the area of public health, there are also differences between infectious and contagious diseases in terms of coping strategies and even a possible declaration of a health emergency, given that contagious diseases can often spread more rapidly.

Always put hygiene first

Knowing the differences between infectious and contagious can be a valuable tool for knowing how to act in order to prevent the transmission of such diseases. In this order of ideas, there are several actions we can take.

However, they all have a common denominator: hygiene. The key is always to maintain proper hygiene with regard to our daily hygiene, with regard to the food we eat, the objects we touch, and the care of our children… In fact, we must be attentive to potential causes at all times.

In the case of these diseases, the agents that cause them are outside our bodies. However, even when they can find ways of entry, we also have many ways to close the doors to infections.