The pattern of disease may be considered local, spreading, or systemic. A local boil may stay localized in a single area of your body; sometimes it may spread in your blood (focal); and become involved in several organs and systems (systemic). The spreading of bacteria in your blood is called bacteremia. What do you call the spreading of fungi and viruses in your blood? (fungemia, viremia) Another term called septecemia is sometimes used to describe the spread and multiplication of Staphylococcus and Streptococcus in your blood.

The initial infection or disease that a healthy organism gets is called the primary infection. Once the host is weakened, a secondary disease may develop. Not all living organisms are equally likely to get a secondary disease. Factors like age (infancy or old age), malnutrition, genetic weaknesses, mental stress, cancers, surgery, chemotherapy, injury, or the AIDS virus may weaken you so you are more susceptible to a secondary infection.

Also humans who are being treated with antibiotics for primary or secondary infections related to bacteria may develop a yeast or protozoal infection. These infections by microbes like Candida (yeast) and Trichomonas (protozoan) are called super-imposed.

When humans are in hospitals, they are often weak and susceptible to hospital-acquired (nosocomial) infections. It is important that hospitals keep good records of nosocomial infications and introduce procedures/actions to keep nosocomial rates below 5%. Bacteria that are known to be involved in nosocomial infections include Staphylococcus aureus (surgical patients), Pseudomonas (burn patients), and E.coli (patients with catheters and other invasive tubes).