Immunocompromised hosts, infection

Caseating granulomas, regardless of location, can undergo liquefaction, spread tubercle bacilli and cause symptoms.2,6 Because of muted or altered symptoms, the diagnosis of TB is difficult and often delayed in immunocompromised hosts.2,3,6 HIV-infected patients may present with only extrapulmonary TB, which is very uncommon in HIV-negative persons. A widely disseminated form of the disease called miliary TB can occur, particularly in children and immunocompromised hosts, and it can be rapidly fatal.17 Immediate treatment is required. 

Hydration and electrolyte balance, often with ORT, are the cornerstone of treatment. The specific circumstances that antibiotics should be considered include high fevers, bloody stools, symptoms longer than 1 week, pregnancy, infection with HIV, and other immunocompromised hosts. 

The number of immunocompromised persons is continually increasing as advances are made in medicine. The life expectancy for persons with cancer, HIV infection, and solid organ or bone marrow transplantation is increasing. Vaccination provides one tool to prevent infection in the immunocompromised host however, the individual s immuno-suppressed state will alter the response to vaccine. In general all vaccinations should be updated prior to the person becoming immunosuppressed, if possible. Once a person becomes significantly immunosuppressed, live virus vaccines should be avoided. 

Lactoferrin, a protein found in secondary granules of polymorphonuclear cells, was observed to be mildly to moderately elevated in the stools of children with endemic cryptosporidiosis [91] and healthy adult volunteers with experimental infection [92], Indeed, in another study of malnourished children in Haiti, cryptosporidiosis was noted to stimulate an inflammatory response, as evidenced by elevated IL-8, TNF-a, lactoferrin, IL-13 and IL-10 [93]. Further studies are needed to elucidate the role of inflammatory mediators in the development of prolonged diarrhea, malabsorption and malnutrition in immunocompromised hosts and children in endemic areas. 

Fantry L Gastrointestinal infections in the immunocompromised host. Curr Opin Gastroenterol 2001 17 40-45. 

Risk factors in the host can give a clue for the causative pathogen e.g. Chronic Obstructive Lung Disease (COPD) - Haemophilus, alcoholism - Klebsiella, HIV - Pneumocystis. The immunocompromised host is also at increased risk for certain fungal (Aspergillus) and viral infections (cytomegalovirus or CMV). Pseudomonas aeruginosa is frequently involved in exacerbations of cystic tibrosis. 

The cancer patient and the HIV-positive patient are the two clinically important groups were the natural defence systems are disturbed either by the disease or by the treatment (chemotherapy, radiotherapy). Infections in the HIV-positive patient are discussed in Chapter 33B. Less prevalent immunocompromised hosts are patients with hypo- or agamma-globulinaemia or patients after splenectomy. These last patient groups with mainly humoral dysfunction generally suffer from infections by encapsulated bacteria S. pneumoniae, H. influenzae and N. meningitidis). In this section we will discuss patients with cellular immune dysfunction, mainly granulocytopenia. 

Important factors in the immunocompromised host predisposing to infection are granulocytopenia, T- or B-cell dysfunction, antibody deficiency. 

Ophtalmia neonatorum by N. gonorrhoeae and Chlamydia trachomatis is acquired during delivery. Contact lens wear predisposes to corneal infections, mostly by Pseudomonas sp. and the ameba Acan-thamoeba and Naegleria. Immunocompromised hosts are predisposed to severe retinitis by CMV and to other intra-ocular eye infections by opportunistic pathogens. 

Prophylaxis is defined as antibiotics used to prevent infection. The reasons to administer prophylaxis can be the same for surgical and non-surgical prophylaxis, and for immunocompetent or immunocompromised hosts alike. These reasons are ... 

Amphotericin B remains the drug of choice in the treatment of invasive aspergillosis, locally invasive mucormycosis, and many disseminated fungal infections occurring in immunocompromised hosts (the patient population most at risk for serious fungal infections). For example, the febrile neutropenic oncology patient with persistent fever despite empirical antibacterial therapy is best treated with amphotericin B for possible Candida spp. sepsis. 

B. Amphotericin B remains the drug of choice in the treatment of disseminated or invasive fungal infections in immunocompromised hosts bone marrow transplant recipients are the most heavily immunocompromised patients encountered in the hospital setting. 5-Flucytosine has no significant activity against Aspergillus spp., and it has bone marrow toxicity as a common adverse effect it should... 

Resistance to acyclovir can develop in HSV or VZV through alteration in either the viral thymidine kinase or the DNA polymerase, and clinically resistant infections have been reported in immunocompromised hosts. Most clinical isolates are resistant on the basis of deficient thymidine kinase activity and thus are cross-resistant to valacyclovir, famciclovir, and ganciclovir. Agents such as foscarnet, cidofovir, and trifluridine do not require activation by viral thymidine kinase and thus have preserved activity against... 

Surgical procedures that necessitate the use of antimicrobial prophylaxis include contaminated and clean-contaminated operations, selected operations in which postoperative infection may be catastrophic such as open heart surgery, clean procedures that involve placement of prosthetic materials, and any procedure in an immunocompromised host. The operation should carry a significant risk of postoperative site infection or cause significant bacterial contamination. 

The major fungal opportunistic pathogens that affect immunocompromised hosts are the yeasts Candida and Cryptococcus, with the filamentous fungi Aspergillus and Fusarium and the dimorphic fungus Histoplasma also causing potentially fatal infections.4 Candida albicans... 

BeckJM. The immunocompromised host HIV infection. Proc Am ThoracSoc. 2005 2 423-427. 

Thom K, Forrest G. Gastrointestinal infections in immunocompromised hosts. Curr Opin Gastroenterol. 2006 22 18-23. 

In contrast to antibacterial antibiotic therapy, inhibition of viral replication is usually difficult to achieve. Therefore preventive strategies, such as vaccination, are frequendy more successful and clinically important. However, vaccines are not available for all viruses furthermore, some viruses, such as Epstein-Barr virus (EBV) and cytomegalovirus (CMV), are ubiquitously present and usually not very pathogenic unless in an immunocompromised host. One strategy to combat viral infecdons in the immunocompromised host is the application of neutralizing mAbs. One such mAh is directed to the F protein of the respiratory syncytial virus (RSV), which afflicts premature newborns with often severe pulmonary infections this mAh appears to be useful in such situations (91). Other mAbs to viral antigens are in development. 

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