A secondary infection is one that occurs when a different infection, known as a primary infection, has made a person more susceptible to disease. It is called asecondary infectionbecause it occurs either after or because of another infection.
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Why Secondary Infections Occur
There are several ways that a primary infection can increase susceptibility to disease, leading to a secondary infection.
Changes to the Immune System
Some diseases can lower the immune system’s ability to fight off harmful invaders like viruses and bacteria. This can make it easier for them to enter and cause a secondary infection.
The opportunistic infections associated withAIDSare a good example of the types of secondary infections that occur when a disease modifies the immune response.They occur because the body can no longer fight off bacteria or viruses that a healthy immune system usually can.
Compromised Skin
Skin infections can compromise the skin’s ability to act as a barrier to the outside world, particularly when they also cause breaks or sores. These can act as entry points for new infections.
For example, when someone scratches a sore from asexually transmitted infection (STI)such asmolloscum contagiosum, it spreads the infection from one part of the skin to another, worsening the primary condition. But it can also make it easier for other bacteria to enter and infect the skin, causing a secondary infection.
Consequence of Treatment
Treatment for a primary infection can also lead to secondary infections. One common example is how antibiotic treatment leaves people with more vaginas more susceptible toyeast infections.
Antibiotics are helpful when treating bacterial infections because they target and kill bacteria. However, in doing so, they kill off both the bad and the good—including normal, healthyvaginal bacteria (flora).
Though the antibiotics may have resolved the primary infection they were intended to treat, the loss of vaginal flora that results means other organisms, such as yeast, can seize the opportunity and multiply without interference.
Individuals may also experience infections at the insertion sites of IVs, catheters, and medical devices, particularly when left in for a long period of time. Technically, these are not secondary infections, as they are due to the equipment rather than a primary illness. However, some may refer to them as secondary infections because they occur after the placement of the device.
Secondary Infection vs. Co-Infection
Secondary infections occur after, or because of, primary infections. However, sometimes people have multiple infections that aren’t directly related to one another at the same time. These infections are often considered to be co-infections rather than secondary infections.
For example, people can be co-infected with bothgonorrheaandsyphilis. Those infections aren’t necessarily related to each other. Instead, they’re both related to similar types of activity. A person who is having condomless sex is more likely to be exposed to STIs. Which STIs, and thus the risk of co-infection, depends on which infections they are living with.
In contrast, if people are diagnosed with an oral yeast infection because of HIV-related immune suppression, that’s a different story. The yeast infection is only possible because of the HIV infection. Therefore, it would be considered to be a secondary infection.
You could make a case for calling HIV acquired in this way a secondary infection, but most doctors wouldn’t. In part, this is because most secondary infections are treated alongside the primary infection. In contrast,HIVis treated as its own separate illness. It’s also because in this circumstance, it’s not clear that the person wouldn’t have acquired HIV anyway. That’s the major difference between a secondary infection and a co-infection. A secondary infection can’t happen without the primary infection. With co-infection, it’s possible that the primary infection just made things easier.
4 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.NIH.AIDS and opportunistic infections.Bikowski JB Jr.Molluscum contagiosum: the need for physician intervention and new treatment options.Cutis. 2004;73(3):202-206.Fabiny A.Ask the doctor. I recently took antibiotics to treat an oral infection and as a result developed a vaginal yeast infection. Can I treat it myself, and what are the most effective options?.Harv Womens Health Watch. 2014;21(13):2.Pasman L.The complication of coinfection.Yale J Biol Med. 2012;85(1):127-132.Additional ReadingKarchmer TB, Giannetta ET, Muto CA, Strain BA, Farr BM.A randomized crossover study of silver-coated urinary catheters in hospitalized patients.Arch Intern Med. 2000;160(21):3294-8. doi:10.1001/archinte.160.21.3294Mirani G, Williams PL, Chernoff M, et al.Changing trends in complications and mortality rates among US youth and young adults with HIV infection in the era of combination antiretroviral therapy.Clin Infect Dis. 2015;61(12):1850-61. doi:10.1093/cid/civ687
4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.NIH.AIDS and opportunistic infections.Bikowski JB Jr.Molluscum contagiosum: the need for physician intervention and new treatment options.Cutis. 2004;73(3):202-206.Fabiny A.Ask the doctor. I recently took antibiotics to treat an oral infection and as a result developed a vaginal yeast infection. Can I treat it myself, and what are the most effective options?.Harv Womens Health Watch. 2014;21(13):2.Pasman L.The complication of coinfection.Yale J Biol Med. 2012;85(1):127-132.Additional ReadingKarchmer TB, Giannetta ET, Muto CA, Strain BA, Farr BM.A randomized crossover study of silver-coated urinary catheters in hospitalized patients.Arch Intern Med. 2000;160(21):3294-8. doi:10.1001/archinte.160.21.3294Mirani G, Williams PL, Chernoff M, et al.Changing trends in complications and mortality rates among US youth and young adults with HIV infection in the era of combination antiretroviral therapy.Clin Infect Dis. 2015;61(12):1850-61. doi:10.1093/cid/civ687
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
NIH.AIDS and opportunistic infections.Bikowski JB Jr.Molluscum contagiosum: the need for physician intervention and new treatment options.Cutis. 2004;73(3):202-206.Fabiny A.Ask the doctor. I recently took antibiotics to treat an oral infection and as a result developed a vaginal yeast infection. Can I treat it myself, and what are the most effective options?.Harv Womens Health Watch. 2014;21(13):2.Pasman L.The complication of coinfection.Yale J Biol Med. 2012;85(1):127-132.
NIH.AIDS and opportunistic infections.
Bikowski JB Jr.Molluscum contagiosum: the need for physician intervention and new treatment options.Cutis. 2004;73(3):202-206.
Fabiny A.Ask the doctor. I recently took antibiotics to treat an oral infection and as a result developed a vaginal yeast infection. Can I treat it myself, and what are the most effective options?.Harv Womens Health Watch. 2014;21(13):2.
Pasman L.The complication of coinfection.Yale J Biol Med. 2012;85(1):127-132.
Karchmer TB, Giannetta ET, Muto CA, Strain BA, Farr BM.A randomized crossover study of silver-coated urinary catheters in hospitalized patients.Arch Intern Med. 2000;160(21):3294-8. doi:10.1001/archinte.160.21.3294Mirani G, Williams PL, Chernoff M, et al.Changing trends in complications and mortality rates among US youth and young adults with HIV infection in the era of combination antiretroviral therapy.Clin Infect Dis. 2015;61(12):1850-61. doi:10.1093/cid/civ687
Karchmer TB, Giannetta ET, Muto CA, Strain BA, Farr BM.A randomized crossover study of silver-coated urinary catheters in hospitalized patients.Arch Intern Med. 2000;160(21):3294-8. doi:10.1001/archinte.160.21.3294
Mirani G, Williams PL, Chernoff M, et al.Changing trends in complications and mortality rates among US youth and young adults with HIV infection in the era of combination antiretroviral therapy.Clin Infect Dis. 2015;61(12):1850-61. doi:10.1093/cid/civ687
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