Infections after renal transplantation

Nosocomial infections [methicillin-resistant Staphylococcus aureus (MRSA), multi-resistant Gram-negative (MRGN), vancomycin-resistant enterococci (VRE) Candida]

The first few months following the NTX are predominantly characterized by nosocomial infections (MRSA, MRGN, VRE, Candida). The differences in prevalence for hospitalized patients with and without immunosuppression and the concomitant rate of nosocomial infections for MRSA and VRE were investigated by Ziakas et al. in a 2014 meta-analysis [20].

It was shown that patients who had undergone an organ transplantation exhibited higher prevalence and infection rates for the two aforementioned pathogens compared to the control group.

Local complications, too, play a special role in this phase as potential sources of infection. These may be caused by the operation itself (frequency of surgical complications after NTX 1%–30% [21]). This may involve the not-so-rare problems with wound healing (27%) and wound infections (5%), as well as anastomotic leakage and lymphoceles near the graft (around 15%), which may also produce bacterial superinfections [22]. But infections that are transmitted directly by the transplanted organ itself may also occur during this period. However, extensive screening prior to the transplantation can minimize these transmitted infections significantly [23], [24], [25]. The CMV status bears mentioning in this context, which will be discussed in greater detail further below.

In addition to known and common infections, there are a number of rare infectious agents. But knowing about these rare pathogens, which are potentially life-threatening for immunosuppressed patients, may be vital.

Lymphocytic choriomeningitis (LCM)

LCM is a single-stranded RNA virus, which occurs mainly in rodents. It is generally transmitted through the inhalation or ingestion of virus-contaminated particles in secretions/excretions of infected animals [26]. Its prevalence in the general population is about 3%.

In immunocompetent people, clinical symptoms generally include only minor flu-like symptoms; in very rare cases, aseptic meningitis or even meningoencephalitis may occur [27]. But frequently fatal outcomes may materialize in immunosuppressed patients. So far, 17 cases have been documented for transplant patients in the literature. Symptoms described in the context of infection are fever, abdominal pain, nausea, vomiting, diarrhea, skin rash, as well as altered mental conditions due to meningoencephalitis [28]. Of the 17 patients affected, a total of 14 died. It is not clear whether the attempted ribavirin treatment actually affected the outcome in the survivors [29].

Rabies

An extraordinary case involved the transmission of rabies by a young donor in Germany, who had become infected with the rabies virus on a trip to India, unbeknownst to her, and who then passed away in Germany following excessive consumption of cocaine and ecstasy. Lungs, liver, kidneys/pancreas, and both corneas were harvested and then transplanted. Except for the vaccinated patient with the liver TX and the cornea recipient, all patients concerned died [30].

Orf, HEV, HTLV1, HCoV-HKU1 and -NL63

The above list of viruses is certainly not complete, but does provide an interesting overview of further rare infections that may occur in connection with immunosuppression and solid organ transplantations. Table 2 gives a brief overview of the clinical manifestations and basic treatment options.

Cytomegalovirus

The CMV status of the donor and recipient plays a special role in the follow-up care of transplantation patients. As already mentioned, CMV is part of the human pathogenic herpes viruses and constitutes a double-stranded DNA virus. The seroprevalence in Germany is at around 35%–50% [31]. In kidney transplant patients, prevalence is >70% [32]. The human CMV pathogen, which has a high host specificity, replicates in fibroblasts, epithelial and endothelial cells, as well as macrophages. Following the primary infection, the virus, like all others in the human herpes virus group, acquires lifelong latency, particularly in CD34-positive hematopoietic stem cells and monocytes. The primary infection frequently occurs in childhood as a result of infectious bodily secretions (lacrimal fluid, saliva, urine, genital secretion, mother’s milk, blood). In the case of transplantation, the source of infection is mostly the donor organ itself (or blood transfusions).

Prior to transplantation, the CMV status of the donor and recipient is tested through an analysis of the CMV-IgG/IgM antibodies, and the individual risk for subsequent CMV infections is determined. The highest risk applies if a CMV-positive donor organ is transplanted in a CMV-negative recipient. KDIGO recommends in its capacity as a nephrology association that all patients – except where the donor and recipient have a CMV-negative status – undergo a prophylactic, virostatic treatment of at least 3 months. Where a patient has received a T-cell-depleting treatment as part of his/her immunosuppressive therapy, the prophylaxis should be continued for at least 6 months [8].

As for diagnosing acute CMV infections, KIDGO recommends an analysis of the pp65 antigen, alternatively also CMV-PCR. The pp65 antigen is a specific CMV antigen (PP: phosphoprotein), which is isolated in lymphocytes from whole blood. For this purpose, the antigen must first be marked by means of antibodies in order to be examined under a fluorescence microscope. The advantage of the pp65 antigen is that it can be detected only in cells that transition from the latency phase to active replication.

But the elaborate analysis also creates bigger problems in routine diagnostics. First, the lymphocytes must be obtained from whole blood by way of a buffy coat. The final assessment by means of fluorescence microscopy often results in significant variations in the assessment that differ from laboratory to laboratory (numerous false-positive/false-negative results with up to 20% in both directions [33]). One problem is also the fact that transplant patients have an overall lower lymphocyte count, which means that the validity is severely restricted by this one circumstance alone. But the analysis of the CMV-DNA by PCR detects both the latent viruses and those undergoing active replication. PCR is particularly important in the detection of the kinetics and in the therapeutic response, as a result of which it is now considered clearly superior to the pp65-Ag analysis [34], [35].

A new test with a high degree of efficiency has become established more recently. It involves the CMV-specific cellular immune response, comparable to the interferon gamma release assay (IGRA) test used in connection with tuberculosis. In this case, too, previously sensitized T-cells of the patient are stimulated with defined pathogen antigens (“immediate early protein 1”, “phosphoprotein 65”), followed by the measurement of the interferon-γ release. This test may prove highly useful in routine CMV diagnostics [36], [37], [38].

Two conditions are generally differentiated in the clinical manifestation of CMV infection. The CMV syndrome most likely corresponds to the manifestation and progression in immunocompetent patients by way of a nonspecific, flu-like syndrome (infection of the upper respiratory tract, fever, fatigue, arthralgia, leuko- and thrombopenia).

The CMV-invasive disease must be distinguished from this, for example, as a severe, gastrointestinal manifestation with nausea, vomiting and abdominal cramps. This may affect the entire gastrointestinal tract (GI tract), with ulcers being detected both in the oral mucosa as well as in the upper GI tract (esophagus, stomach, etc.). It is not rare for bloody diarrhea to occur at the same time, which is then a manifestation of a severe CMV colitis. In the extreme case, a necrotizing colitis with toxic megacolon may develop as a complication [39].

CMV retinitis is particularly feared. Patients complain of blurred and impaired vision, while they experience no pain in the eyes. Complete blindness may be the outcome if treatment is delayed or not initiated. However, CMV-associated organ affections may also affect the lung (interstitial pneumonia), liver, pancreas and the kidneys.

It is also known that the cytomegalovirus, apart from the direct disease, may also facilitate infections with other pathogens (EBV, HSV, invasive mycoses) [40].

The effect of an active CMV infection, in the sense of a triggering of possible graft rejection, is of no less significance. Cytokine-mediated processes result in an increased expression of the HLA-class II antigens, initiating acute and subacute rejection responses [41], [42].

The most crucial risk factor for the development of a severe CMV infection is seronegativity in the recipient when the organ donor is CMV-positive (CMV mismatch).

Just as important, however, are also immunosuppressive regimens which provide for T-cell-depleting antibody treatment in connection with the initial induction. Obviously immunosuppressive protocols that contain mTOR inhibitors provide a certain degree of protection against CMV infections [43].

The broad use of virostatic prophylaxis with valganciclovir has proved widely successful in preventing CMV infections in recent years. Still, where the high-risk constellation (donor is CMV-positive/recipient is CMV-negative) is concerned, 20%–30% of patients develop a CMV disease after discontinuation of the prophylaxis [44].

The treatment of choice in the case of an active CMV disease is valganciclovir/ganciclovir, administered intravenously for 8–10 days (followed by oral treatment with weekly PCR virus load checks). Apart from the virus load in the blood, a PCR analysis should also be conducted on other body fluids (bronchoalveolar lavage, CSF in the presence of relevant symptoms). CMV nephritis may also occur in connection with the CMV infection, but overall is very rare (especially as CMV glomerulopathy and interstitial nephritis). A CMV-PCR from urine is recommended in addition to direct nephropathologic diagnostics (cytopathic changes in the epithelial and tubular cells) in these cases [45].

(Immuno-)histopathologic assessment with detection of typical giant cells helps to complete the diagnostics.

In therapy-refractory cases, a reduction in the immunosuppressive treatment should be considered, possibly after resistance testing [46]. Furthermore, intravenous immunoglobulin G (IVIG) can be administered with a high CMV-IgG titer in addition to other virostatic drugs (foscarnet or cidofovir) [47].

Tuberculosis

Latent tuberculosis has moved to being the center of attention in the wake of the migration flows in recent times from various countries (Syria, Afghanistan, Pakistan, sub-Saharan Africa).

The incidence of tuberculosis in Germany has increased dramatically in recent years. The Robert Koch Institute (RKI) recorded 5865 new cases of tuberculosis cases in 2015, which is equivalent to an increase of 29% over the previous year [48]. For this reason, the mandatory screening tests prior to a kidney transplantation must be particularly thorough, because a significant increase in the incidence and prevalence of tuberculosis will most likely occur in the following years as well, both in the general population of people with healthy kidneys and in the population of patients requiring dialysis.

In this context, it must be emphasized in no uncertain terms that the number of new cases of tuberculosis involving patients after a solid organ transplantation has already increased significantly (frequency up by a factor of 20–74), that is, aside from the generally elevated incidence and prevalence of tuberculosis abroad, and thus also in people with a migrant background [49]. It should be kept in mind that the risk of tuberculosis also depends on the type of organ transplantation (liver TX: 0.7%–2.3%, heart TX: 1%–1.5%, kidney TX: 1%–15%) [50].

At any rate, the two T-cell-dependent immunological tests (tuberculin-skin test and IGRA) (alternatively Elispot, which is considered equivalent to IGRA based on previous studies [51]) should be carried out both as part of the screening prior to a transplantation and if an active tuberculosis following NTX is suspected. The limited sensitivity of the tests with respect to immunosuppression (specific T-cell suppression by calcineurin inhibitor) should be considered in the clinical assessment of the laboratory findings [52]. The PCR, thanks to its high sensitivity also for transplant patients, represents a very valuable diagnostic tool, but false-positive findings are generated in a not-so-small number of cases [53].

On the whole, when testing for active tuberculosis in patients following NTX, it is all the more important to push for direct evidence of pathogens from tissue and body fluid samples, not least in view of the diagnostic gaps in the aforementioned tests.

Parasitoses

Some of the parasitoses described in the follow-up care of transplant patients are detected mainly in subtropical-tropical and/or Mediterranean regions (Strongyloides stercoralis, Trypanosoma cruzi, Leishmania). Nevertheless, in this context, too, one must expect non-endemic infections in light of the most recent epidemiological developments (see above).

Strongyloides stercoralis

Autochthonous cases of strongyloidiasis are very rare in Europe, but one also often encounters chronic infections among migrants. Therefore, the preparations for a transplantation do require a specific anamnesis with respect to the country of origin.

The special infection cycle (2-phase; 1^st phase: Invasion of the skin with migration into the lungs, followed by ingestion into the small intestine. Second phase: Multiplication in the small intestine with subsequent excretion of infectious larvae) of this parasitosis [54] plays a significant part in repeated auto-infection. In other words, patients remain infectious even long after they have left the endemic country. What may prove particularly lethal after a transplantation is the fact that, apart from the existing immunosuppression, the frequent administering of steroids may act as a booster for infections, because the steroid stimulates the growth of S. stercoralis [55].

Babesiosis

Babesiosis is very rare in Germany. Still, there are documented infections in Germany and Europe with defined strains (Babesia microti, B. divergens and B. venatorum) [56], which may manifest with particular vehemence also in patients who have undergone an organ transplantation [57]. The number of unreported cases is surely much higher given the unknown nature of the disease. At the very least, the possibility of babesiosis should be taken into account, after ruling out common causes, in each case of febrile hemolytic anemia.

In addition to serological and laboratory test methods [PCR, immunofluorescence test (IFT) and antibody detection), particularly the microscopic assessment of the blood smear with detection of the typical Maltese crosses is of diagnostic significance [58].

Polyoma virus infections [BK nephropathy, progressive multifocal leukoencephalopathy (PML)]

Two types of the polyoma virus, in particular, play a leading role in transplantation medicine: the human polyoma virus type 1 (BK virus) and type 2 (JC virus). The seroprevalence in Germany is at around 60%–90%. The BK virus was isolated for the first time in 1971 in the urine of a kidney transplant patient with the initials BK [59].

For immunocompetent people, the BK/JC virus does not pose a clinical relevant infection. The special aspect here is that the virus remains in the urinary tract and CNS for a lifetime after the primary infection (infection in childhood at approximately 85%), and may cause considerable complications in connection with immunosuppression [60].

First, the virus ascends to the proximal tubule. Due to the virus’s presence in the blood, this is followed by interstitial nephritis with possibly severe tubulitis, which counts among the most common causes for losing a transplant (BK nephropathy) in the first 2 years, aside from acute rejection following the transplantation. The histopathologically described tubulitis cannot be differentiated morphologically from an acute rejection response. The infection can be detected only by means of an additional, immuno-histochemical staining of the tubule nuclei with antibodies against the “SV 40 Large T-antigen” [61]. Meanwhile, the routine PCR screening for the BK virus has become a fixture in the first 2 years. Depending on the viremia (such as the result of the kidney biopsy), immunosuppression is then reduced and/or modified. There still is no virostatic treatment to date.

The JC virus infection in the total population is at >90%, with the progression in healthy individuals being clinically inapparent [62].

The risk of a JC virus infection in connection with solid organ transplantations is <1%. Patients are identified on the basis of early cognitive deficits. Subsequently, patients may develop focal neurological deficits, ataxia, visual impairment and seizures [63]. The cMRT reveals multiple lesions in the white substance. The diagnosis is based on direct virus detection by means of PCR from blood and especially cerebrospinal fluid (CSF). Sensitivity is about 80%. In case of doubt, a direct brain biopsy may be required [62].

The mortality of the disease is very high, at >80%. The only effective treatment option is the reduction of immunosuppression [64].

Pneumocystis jiroveci (PjP)

The incidence of developing a PjP is at around 5% for transplant patients. Symptoms may be rather mild at the onset, and may not be able to be distinguished from a minor flu-like infection. Patients complain of coughing, fever and dyspnea. The chest X-ray may be inconspicuous at the outset. The classical, interstitial-bilateral changes are detected only in the computer tomography scan (without contrast media). A special characteristic of PjP pneumonia is early-onset hypoxemia [65].

The diagnosis is arrived at via the direct microscopic detection of the pathogen from the BAL and/or via PCR [66].

The first-line treatment, for both the prophylaxis and acute infection, involves trimethoprim-cotrimoxazole.

The prophylactic administering of cotrim not only protects against PjP, but also against toxoplasmosis, Isospora belli, Cyclospora caytanensis and against many Nocardia and Listeria species [67].

Candida and Aspergillus

The most common mycoses in our latitudes are Candida spp. and Aspergillus spp. Taken together, they account for around 65% of all proven mycoses.

It should be noted that invasive aspergillosis affects kidney transplant patients much less often than patients having undergone under solid organ transplantations [68].

When a mycosis is suspected, it is key to determine whether this involves a superficial (e.g. skin, mucositis, thrush, asymptomatic candidiasis) or invasive mycosis (IM). IM-related mortality is estimated to be 25%–80% [69].

The risk factors for the development of invasive aspergillosis have been described well in various studies [70], [71].

These factors include: “Previous stay in intensive care”, hemodialysis, “treatment with high doses of steroids/aggressive immunosuppressive regimen (T-cell-targeted treatment/e.g. ATG)”, “concomitant latent or manifest CMV infection” [72], “type of organ transplantation” (lung>liver>heart>kidney [73]) and “antibiotic pretreatment”, with the latter appearing to be instrumental in the development of IM [71].

Entry points for Candida spp. are the gastrointestinal and urinary tracts, as well as foreign bodies, such as bladder catheters, central venous line catheters, drains and surgical wounds. In rare cases, candidiasis or aspergillosis may manifest directly in the organs (lung, heart valves, eyes, meninges, etc.).

An IM diagnosis is considered confirmed if, in addition to the clinical picture and any supporting radiological diagnostics (e.g. round lesions with “Luftsiches” signs in the CT of the thorax, dense and sharply delineated lesions with and without halo signs), it is successfully detected by culture and/or histopathology in test materials (blood, urine, bronchoalveolar lavage, biopsies). Unfortunately, direct culture-based evidence is found only in a relatively small percentage of patients (e.g. maximum of 50% from a bronchoalveolar lavage in the presence of IM [74]).

Indirect indications of IM are provided by serological and laboratory-chemical markers. In this case, it is primarily the antigen components of the fungi that are analyzed. The detection of the Aspergillus antigen (galactomannan) in blood and/or CSF [75] has become the prevailing method, and is considered a highly sensitive marker that is detectable even in an early phase of IM.

Galactomannan is released as a polysaccharide-cell-wall component during fungal growth and can be detected in the smallest of concentrations. If there is a high level of clinical suspicion of IM, a one-time negative test should be repeated due to time-inconsistent antigenemia.

According to the diagnostic criteria of the European Organization for Research and Treatment of Cancer (EORTC) and the National Institute of Allergy and Infectious Diseases Mycoses Study Group (MSD) consensus group, detection of the Aspergillus-Ag above the cut-off value indicates a probable diagnosis of invasive aspergillosis [76].

However, false-positive test results may be obtained in connection with antibiotics such as specific penicillins (amoxicillin, amoxicillin/clavulanic acid, piperacillin, piperacillin/tazobactam, etc.). This may be caused by contamination with fungal residue during the production process [77]. The test result can, in fact, be falsified even several weeks after a previous antibiotic treatment. Using PCR with aspergilli is possible, but is not considered a standard method [78]. Antibodies can also be analyzed as part of the diagnostics, but plays only a minor role due to the diminished and delayed humoral immune response in the group of immunosuppressed patients.

A direct detection by culture and/or histopathology should always be sought, also when candidiasis is suspected. The commercially available serological tests (Cand-Tec^®-Test; Pastorex-Candida; Platelia-Candida) for the detection of the Candida antigens can complement the diagnostics in a meaningful manner. Sensitivity (around 50%–95%) and specificity (70%–80%) vary relative to the test method used [79].

The means of first choice in the treatment of candidemia or invasive candidiasis are fluconazole [note: resistances or reduced response rates for some Candida spp. (e.g. C. glabrata, C. krusei)], caspofungin, anidulafungin and micafungin.

In the treatment of severe invasive aspergillosis, the primary use of voriconazole, sometimes in combination with an echinocandin, has proved successful [80]. Alternatively, treatment may also involve liposomal amphotericin B [76] or isavuconazole [81].

Cryptococcus, Mucor, Blastomyces, Histoplasma

Cryptococcosis is triggered by the yeast-like, encapsulated fungus Cryptococcus neoformans. In immunosuppressed patients, the pathogen either reaches the lung via the respiratory tract and triggers pneumonia or overcomes the blood-brain barrier, causing meningitis or meningoencephalitis in the CNS. In diagnostic terms, the pathogen can be detected by imaging methods as well as by means of biopsies, blood and CSF samples or punctates. The staining of the typical encapsulated yeast organisms can be detected in the CSF. Antigen analysis is also possible as an addition, but plays a minor role in the diagnostics. Once the diagnosis of an infection has been confirmed, the immunosuppression should be reduced where possible. In addition, an initial treatment with liposomal amphotericin B and flucytosine is recommended for patients with a solid organ transplant [82]. Overall, though, cryptococcosis is rarely observed in kidney transplant patients [83], [84].

The Mucorales represent another family of filiform fungi, which are generally saprophytic. Some members of the family are pathogenic in people with a weakened immune system and can cause invasive infections, which are generally associated with a high degree of mortality due to the fulminant progression. Especially feared are pulmonary and rhino-cerebral manifestations. Starting with a fungal disease in the nasal sinuses, the condition may frequently move to the brain. An angio-invasion with subsequent thrombosis of the vessels is also frequently observed. The diagnosis is made by way of microscopy and by means of a fine tissue examination. It is possible, and highly recommended, to set up a culture for the diagnosis and analyzing resistance.

A quick start to the treatment with liposomal amphotericin B is essential to the patient’s survival [85], [86], [87].

Blastomycosis is caused by various pathogens, varying by geographical region. The European type (C. neoformans) has already been discussed. Blastomycoses in North and South America are triggered by Blastomyces dermatitidis and Paracoccidioides brasiliensis, and represent a serious threat even to immunocompetent people. Mild cases are treated with itraconazole, particularly in the absence of a CNS manifestation [88]. The use of liposomal amphotericin B is recommended in cases involving severe clinical symptoms and disseminated manifestation [89].

Histoplasmosis is caused by Histoplasma capsulatum. Its geographic distribution includes India, Africa, Southeast Asia, the Midwest of the USA and Latin America. But there are also cases in other regions (Middle East, Israel, Turkey) [90], [91].

The highly contagious pathogen is inhaled by dust or may enter open wounds. Accordingly, it can trigger clinically serious pulmonary infections or wound infections.

Detection by culture is very difficult. Antigen determination is possible and is also used as part of the diagnostics [92], [93]. Histoplasmosis is also treated with liposomal amphotericin B and itraconazole [89].

Influenza A

Seasonal influenza A may be a serious complication for immunosuppressed patients. In other words, all kidney transplant patients should be vaccinated despite the low degree of immunization [94]. Where the condition is suspected, a treatment with neuraminidase inhibitors should be initiated within 24 h.

Nocardiose

With continued cotrim protection, as already mentioned, listeriosis and nocardiosis occur much less frequently.

The development of a nocardiosis (usually with a pulmonary infection after inhalation) appears to be favored by a high-dose steroid regimen, the use of calcineurin inhibitors and an active CMV disease. One problem in this context is the fact that there is not yet a reliable serological test for the diagnosis of nocardiosis, which means that taking a tissue sample is the only way.

HIV infection and kidney transplantation

Since the introduction and consequent further development of highly effective antiretroviral therapy, an HIV infection is no longer considered a contraindication for a kidney transplantation. HIV-infected kidney transplant recipients now exhibit excellent long-term trends with respect to overall mortality and transplant survival [95]. Predictors for a good outcome of a transplantation are a well-controlled HIV infection with CD4 cell counts above 200/μL, as well as a virus load below the detection limit [95], [96], [97].

What must be closely and strictly monitored, though, are the potential and numerous drug interactions between the HAART medication and the immunosuppressants (e.g. calcineurin inhibitors may have to be reduced to approximately a quarter of the customary dose when using protease inhibitors [98]. More recently, however, there have also been immunosuppressive protocols that do not interact with virostatic medication (combinations from basiliximab, calcineurin inhibitors, mycophenolate mofetil (MMF) and steroids [99]).