Infection occurs when a disease-causing germ such as a bacteria, virus or fungus invades the body. To become infected, you must catch the germ (exposure) and have the ability to become infected (susceptibility). Susceptibility is more complicated than exposure. We are all susceptible to infection by thousands of different germs. The purpose of the immune system is to prevent infection by recognizing germs and eliminating or disabling them before they can cause infection.
People with immunodeficiency get the same kinds of infections that other people get—ear infections, sinusitis and pneumonia. The difference is that their infections occur more frequently, are often more severe, and have a greater risk of complications.
We live in a sea of germs, and everyone gets an infection at least once in a while. However, while most people can recover on their own from most infections, some people experience recurring infections that require antibiotic treatment.
Exposure and susceptibility to infections
Infection occurs when a disease-causing germ, such as a bacteria, virus or fungus, invades the body. To become infected, you must catch the germ (exposure) and have the ability to become infected (susceptibility). People with a lot of contact with others, such as elementary school teachers or salespersons, are more likely to be exposed to increased numbers of germs.
Susceptibility is more complicated than exposure. We are all susceptible to infection by thousands of different germs. The purpose of the immune system is to prevent infection by recognizing germs and eliminating or disabling them before they can cause infection. Remarkably, the immune system has the unique ability to learn the “face” of a germ and remember it forever. Some germ families have faces that are so similar that when your immune system learns the face of one member of the family, it protects you from infection by any member of that family. Other germ families are so different that the immune system must learn each face individually. Once your immune system has learned the face of a particular germ and successfully battled it, you are much less susceptible to infection caused by that germ.
The first line of defense against infection is located where the body has contact with the rest of the world—the skin—as well as the membranes that line the respiratory system and digestive systems. Clearly, a cut on the hand is more likely to get infected than unbroken skin. Similarly, irritation, swelling and injury to the mucus membranes lining the nose, sinuses and lungs provide a fertile ground for disease-causing germs. If you have year-round allergies to dust mites, pollen and mold, you may have some injury to your mucus membranes, which can, in turn, increase your susceptibility to infection. Once a germ has entered the body, your immune system springs into action.
Common infections
The most common infections are viral respiratory tract infections—colds. Typically, cold symptoms last five to 10 days. If a child gets 12 colds a year, each lasting less than 10 days and usually improving without needing treatment with antibiotics, there is not usually a cause for concern. It may seem, however, that the child is sick half the time—because he or she is! These viral infections are a result of the close contact that young children have with other infected children and the fact that their immune systems are relatively immature. Once a child’s immune system learns the faces of many of the germs that cause such colds, the child will get infected less frequently.
Another infection, strep throat, is also a “social disease” that children and adults catch because they are in close contact with infected individuals. Although we don’t completely understand why some people get strep throat frequently, we know that recurrent strep throat is rarely an indicator of a weak immune system.
Many people confuse allergic rhinitis, or “hay fever,” which causes stuffiness, nasal itch and a runny nose that lasts for weeks, with a cold or sinus infection. Your allergist/immunologist can help you differentiate allergies from infection, or know when both are present at the same time. Once the possibility of allergy is eliminated, your allergist will consider if your infections are a simply a result of high exposure to other people with infections, or if these infections are warning signals of an immune system problem called immunodeficiency . There are many forms of immunodeficiency and while some are very severe and life-threatening, many are milder but still important enough to cause recurrent or severe infections.
Signs of Immunodeficiency
People with immunodeficiency get the same kinds of infections that other people get—ear infections, sinusitis and pneumonia. The difference is that their infections occur more frequently, are often more severe, and have a greater risk of complications. Furthermore, the infections usually do not go away without using antibiotics and often recur within one to two weeks after antibiotic treatment is completed. These patients frequently need many courses of antibiotics each year to stay healthy. Patients with some forms of immunodeficiency are more likely than other people to develop infections inside certain areas of the body, such as the bones, joints, liver, heart or brain.
In most cases, the frequency of infection is the most important issue, but sometimes a single infection with an unusual germ is enough to trigger the need for the doctor to perform a thorough immunologic evaluation of the patient.
So, how many infections are too many? Allergist/immunologists often use the frequency of the use of antibiotics to mark the frequency of significant infections. Older children and adults with healthy immune systems seldom require antibiotic treatment. However, for the reasons mentioned above, many younger children receive several courses of antibiotic therapy each year. Therefore, the number of ear infections that may be “normal” in a child under 5 years of age is clearly abnormal in older children and adults.
General guidelines for determining if a patient may be experiencing too many infections are:
- The need for more than four courses of antibiotic treatment per year in children or more that two times per year in adults.
- The occurrence of more than four new ear infections in one year after four years of age.
- The development of pneumonia twice over any time.
- The occurrence of more than three episodes of bacterial sinusitis in one year or the occurrence of chronic sinusitis.
- The need for preventive antibiotics to decrease the number of infections.
- Any unusually severe infection or infections caused by bacteria that do not usually cause problems in most people at the patient’s age.
If you have any of the conditions noted above, your allergist/immunologist will consider if you need to be evaluated for immunodeficiency. Very often, this evaluation may give reassuring results and even improve your immunity since immunizations may be part of the evaluation. If an immunodeficiency is detected, early treatment prevents complications of infections that then contribute to making other infections worse and more difficult to treat.
Although small children are expected to have a large number of respiratory infections, it is important to be vigilant in this population for unusually frequent or severe infections. This is because the most serious immunodeficiencies usually become apparent during the first years of life. Signs that a physician should consider examining a patient further for possible immunodeficiency include persistent fungal infection of the mouth or skin, prolonged diarrhea or persistent cough. If a primary care or family physician believes that a patient’s infections exceed the normal range, the doctor should consider referring the patient to an allergy/immunology specialist.
The most common forms of immunodeficiency are caused by defects in your ability to produce blood proteins called antibodies. Antibodies are proteins that attach to germs and help the body eliminate them. Simple blood tests can measure the number of antibodies you are producing. To fully evaluate your antibodies, it may be important to measure specific antibody responses by giving you diptheria, tetanus and pneumococcal (pneumonia) vaccines and performing a blood test before immunization and three to four weeks later. Skin tests or more specialized blood tests can diagnose other forms of immunodeficiency. Allergy skin tests are sometimes done because allergies often contribute to infection susceptibility, and many patients with immunodeficiency also suffer from allergies.
Treatment of recurrent infections
So, what can be done about recurrent infections? The key to minimizing problems with infections is to understand the basis of the immunodeficiency by using appropriate testing. Once your physician properly diagnoses your immunodeficiency, he or she can provide treatments that help you lead a more full life. Treatments are available for many immunodeficiencies. For example, the most common forms of immunodeficiency are often treated with infusions of antibodies called intravenous immunoglobulins (IVIG). IVIG essentially replaces the antibodies that your body is unable to make. Your allergist/immunologist is experienced in using such treatments, which help minimize infections, speeds recovery, and strengthens the immune system.
Patients who have a family history of immunodeficiency or unexplained severe infections should also sometimes be evaluated for an immunodeficiency, even before they develop any infections. This may be done at birth in some cases. An allergist/immunologist will be able to counsel patients about the risk of other family members being carriers of or being affected by an immunodeficiency. Other patients may have immunodeficiencies that can be recognized before the development of infections because of the presence of other abnormalities, such as congenital malformations. It is important to recognize these situations since infections and their complications may be prevented by an early diagnosis and prompt institution of corrective measures.
