CD4 count and PCR key to predicting relapses of leishmaniasis

A group of French investigators have proposed guidelines for secondary prophylaxis of leishmaniasis among people with HIV. They report in the May 1^st issue of the Journal of Acquired Immune Deficiency Syndromes that CD4 cell counts and PCR assays for parasite detection are predictors of relapse, and when used together may help guide when patients can safely stop secondary prophylaxis.

Visceral leishmaniasis, caused by the parasite Leishmania infantum, occurs in parts of India, China, Russia, Africa and South America, and also in Spain, Italy and southern France. In people with AIDS, clinical signs of the infection can be unusual and so laboratory confirmation is needed. Direct examination of bone marrow smears for the parasites, called mastigotes, or in vitro culture of blood or bone marrow samples are considered the gold standard. PCR assays testing for the presence of parasite genetic material in blood or bone marrow have also been developed.

In cases of HIV, Leishmania infection is associated with a high rate of relapse and poor response to treatment and so patients often require secondary prophylaxis and close follow up. Having predictors of relapse would aid in clinical management, and so Bourgeois and colleagues at two university hospitals in southern France conducted a prospective study to identify factors associated with relapse and to test the value of PCR-based assays in predicting disease recurrence.

The small cohort comprised 27 patients with AIDS who had a diagnosis of leishmaniasis, were treated with amphotericin B for the infection, and then put on secondary prophylaxis with the same drug. Patients also received antiretroviral therapy to control their HIV infection. The group was then followed every three or six months for a median of 51 months (range five months to nine years), during which time researchers performed routine lab measures including PCR monitoring of blood samples for the presence of Leishmania. They also recorded relapses, which were diagnosed by clinical signs and confirmed by biologic tests, either gold standard tests or PCR.

During follow up, 16 (59%) of 27 patients relapsed for a total of 38 clinical relapses. The first relapse generally occurred during the first 18 months and always when the patient was still on secondary prophylaxis.

When the investigators analyzed data for predictors of relapse, the absence of anti-HIV treatment at diagnosis and CD4 count below 100 cells/mm³ at diagnosis were associated with a significantly lower risk of relapse (p = 0.036 and p = 0.006, respectively). Factors not associated with relapse included advanced HIV disease, HIV viral load and other blood cell counts.

CD4 count during follow up was also associated with occurrence of relapse. All relapses occurred when CD4 counts were below 200 cells/mm³, and 33 (87%) of 38 occurred when counts were below 100 cells/mm³. The investigators note that 25 (65.7%) relapses occurred when the patient was receiving secondary prophylaxis, suggesting prophylaxis does not provide complete protection.

Among the 27 patients in the study, 18 had PCR results become negative within the first 6 months after treatment. Of these, seven patients relapsed once or twice. For all 18 patients, PCR remained negative outside of relapse periods in almost all, 268 of 273, cases. In the remaining five cases, there was a single positive PCR blip that was followed by negative PCR results. There were no clinical signs of disease in these five instances and treatment was not changed.

In these 18 patients, when PCR results became negative after a relapse and remained negative for at least 18 months, there was only one relapse.

Nine of 27 patients had persistent positive PCR results after treatment of primary infection. These patients accounted for 29 (76%) of the 38 cases of clinical relapse. These positive PCR results were associated with positive cultures in only 30 of 78 cases. Thus, positive PCR results were seen when there were no other signs of relapse, and the investigators reported that positive predictive value of PCR for relapse was low, 42.5%. However, they point out that in these nine cases the rate of relapse was 3.2, compared with 0.5 in the 18 patients with negative PCR results.

Putting these findings together, the investigators argue that, “whereas a positive PCR test result is not sufficient to assert a clinical relapse, the presence of 2 or more successive positive PCR test results during relapse-free periods constitutes a highly predictive risk factor for relapses. Conversely, our data suggest that negative PCR test results during more than 18 months may constitute a practical indicator for stopping secondary prophylaxis while maintaining a low and stable risk of relapse.”

Their proposed series of guidelines use both CD4 cell counts and PCR results to guide decisions around secondary prophylaxis in people with HIV receiving antiretroviral therapy. Secondary prophylaxis for leishmaniasis may be discontinued when either:

• PCR results are negative and CD4 cell counts are stably above 200 cells/mm3 for at least six months
• When CD4 counts are below 200 cells/mm³ but PCR results have been negative for at least 18 months

In both cases, follow up should include ongoing PCR on blood samples to detect parasite recirculation. Conversely, they suggest, positive PCR results in the absence of clinical signs of relapse indicates that prophylaxis should be maintained, regardless of CD4 cell counts.