Infections Related To Impaired Immunity

Definition
Patients who have impaired immunity as a result of their underlying illness and/or as a result of treatment with immunosuppressive drugs or chemotherapy drugs are often called immunocompromised hosts (ICH). The ICH patient population is heterogenous and includes the following patient groups :

  • Patients born with primary immune deficiency syndromes
  • Patients undergoing treatment for cancer
  • Patients with underlying autoimmune and autoinflammatory disorders
  • Patients with HIV infection / AIDS
  • Patients on systemic steroids, biologics and other immunosuppressive medications
  • Patients who are solid organ or stem cell transplant recipients

Patients at extremes of ages and/or with underlying chronic diseases like renal failure, diabetes, splenic disorders including splenectomy, chronic liver diseases also have impaired immunity, they are not called ICH and will be considered separately.

Epidemiology
Patients with impaired immunity are at a higher risk for infection by the “usual” pathogens (like influenza, pneumococcal disease) and also by unusual organisms like certain viruses, fungi or parasites. The list of possible pathogens is huge and the more immunosuppressed the patient, the larger the list.

Clinical
ICH with infection will present in the same manner as other usual patients and will have:

  • Fever, chills and shakes (rigors)
  • Symptoms referable to the organ or tissue affected by the infection

The difference is that the pace of illness is often more rapid and clinical deterioration may occur more rapidly as the immune system in these patients may not be able to cope with even common mild infections.

Diagnostic Tests
Fever in ICH will require further investigations. Besides standard blood counts and general biochemistry, culture of blood and body fluids and X-rays of organs affected are often required.

Treatment
Depending on the severity of underlying condition and current infection, early antibiotic therapy may be prescribed whilst awaiting results of investigations. The approach of starting antibiotic therapy early in ICH is based on the premise that ICH have suboptimal immune responses that are unable to cope with otherwise simple and trivial infections.

Prevention
Immunization against vaccine preventable diseases has been under-utilized in ICH. There are specific recommendations on vaccination of ICH and there has been greater awareness on the need to immunize these patients to prevent infection. For example, stem cell transplant patients have a 120-150 fold higher risk of invasive pneumococcal disease than the general population. Therefore, vaccination against pneumococcal disease is critical in ICH. As expected, ICH by virtue of their condition or treatment may not respond as well to immunization when compared to the general population. The vaccine dose and frequency are individualized and referral to a knowledgeable and skilled physician is necessary.

There is no vaccine for every infection that the ICH may be at risk for. In selected patients who have very poor immunity (e.g. allogeneic stem cell transplant patients in the early post-transplant period), prophylactic antimicrobial agents may be prescribed to prevent common bacterial, fungal and viral infections.

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