Despite numerous descriptions of the infectious and non infectious causes of IRIS, the overall incidence remains largely unknown, particularly in many resource-limited areas and pediatric populations. There is no consensus on case definitions for IRIS in children, yet we continue to recognize probable IRIS-like presentations. We report a cross-sectional prevalence of IRIS of 38% during the first 6 months of ART in Uganda. The majority of these events (77%) would be considered unmasking IRIS manifestations. The vast majority of these events were atypical in having exaggerated clinical presentations, though the contribution of ongoing immunosuppression cannot be discounted. The overall, very important implication is that pediatric HIV care consists much more than simply delivering antiretroviral medications to children and that in the first few months of ART, subclinical infections are frequently unmasked. This should be an expectation for patients, their caregivers, healthcare workers, and policy makers.
The ability of comparison of this cross-sectional study with other cohorts is limited, as the majority of studies have been retrospective in design and/or focused on adults, with a few exceptions [9
]. The prevalence of IRIS in this Sub-Saharan African cohort appeared to be higher than the 23.4% IRIS prevalence in hospitalized Thai children [9
]. Another retrospective pediatric cohort study reported an IRIS incidence of 20% among 91 children in Lima, Peru [16
]. Retrospective design has some limitations with incomplete documentation leading to misclassification of such a relatively new entity as IRIS. Our study does match up similarly to the 41% incidence of probable and possible IRIS prospectively observed in a large adult cohort in Durban, South Africa [17
The high prevalence of IRIS in this study population is possibly attributed to late presentation and a high background burden of subclinical infections. Diagnosis of HIV-infection in infants is complicated, and in resource-limited areas often delayed, due to lack of diagnostic resources and lack of parental awareness of their own HIV-status and thereby the infant’s risk. The result is continued late presentation of HIV-infected children seeking HIV care only after developing advanced immunosuppression and presenting with one or more OIs. This is reflected in this study population as the majority (70%) started ART with baseline CD4+% <15% indicative of severe immunosuppression and at risk of OIs. Second, in this resource-limited environment, children are frequently exposed to high background of infectious disease from OIs, environmental, and childhood vaccine preventable diseases. In the absence of comprehensive pre-ART screening, sub-clinical infections are likely frequently present when starting ART.
In this study, the peak time of IRIS occurrence was within the first month of commencing ART. In the Shelburne study most IRIS events presented in the first 60 days after ART initiation and Bakeera study the median time TB-IRIS occurred was at 14 weeks [9
]. The probable reason why IRIS may occur earlier in children than adults is two-fold. First, children have a more robust improvement of their immune system with ART than adults, specifically children often achieve a 10-fold CD4+
T-cell increase, mainly of naïve T-cells [18
]. In our study a rise of ≥25 CD4+
cells/µL from baseline carried a 3-fold risk of having an IRIS event, and the CD4 increase was most marked in the first month on ART when most IRIS events occurred. Our analysis did not adjust for time on ART. Thus, even though IRIS cases had a shorter duration of ART than controls without IRIS, the CD4 response was more robust in IRIS cases.
Demographic factors also were associated with IRIS for both clear and unclear reasons. Increasing age was associated with IRIS, peaking in children who were 5–12 years of age. Age correlated with the degree of immunosuppression, thus on multivariate analysis, age was not an independent risk factor. Increasing age also represents increasing time at risk of TB exposure. Older children also had easier clinical history taking making it easier to diagnose IRIS-related events. Sex was also associated with IRIS. In our study, the prevalence of IRIS in males was higher, and remained so in multivariate analysis. This is similar to Shelburne et al who reported a 2.65-fold risk in males for IRIS [9
], yet differs from other prospective adult cohorts in Africa [19
]. The biological plausibility of sex as a risk factor for IRIS in children is unknown.
IRIS can manifest with a wide variety of clinical symptoms, depending on the target of the inflammatory response thus the resulting clinical manifestation of IRIS depends on the prevailing infections in the locality. In our study multiple and varied presentations of IRIS occurred. There were 86 clinical episodes of IRIS characterized as 18 distinct clinical scenarios which occurred in 62 children. The clinical scenarios involved either unusual manifestations of a previously treated OI or unmasking of a previously subclinical infection [1
Considering that Uganda is a high TB burden country, it was not surprising that unmasking TB-IRIS was the most common single clinical scenario of IRIS. The proportion of TB-IRIS events (29%) was similar to the proportion of mycobacterial-related IRIS observed in Thailand (44%) and Peru (35%) [8
]. In adult studies, paradoxical TB-IRIS manifestations primarily occur within the first 3 months of ART and have been reported as: fever, lymphadenitis, subcutaneous abscesses, pulmonary infiltrates, or inflammatory masses [23
]. In our pediatric cohort, the most common symptoms of TB-IRIS were fever, cough, and lymphadenopathy. The 15% overall incidence of ART-associated TB in this study was similar to adult studies[11
], and similar to the 17% incidence previously reported by Bakeera- Kitaka et al from Kampala, Uganda and higher than the 9% incidence reported in Chiang Mai, Thailand and 6.5% in Peru [9
]. The higher prevalence of unmasking ART-associated TB in Uganda than in Thailand or Peru may reflect the increased burden of TB in Sub-Saharan Africa.
Our finding that cough for >7 days at the time of enrolment was associated with IRIS is not surprising since TB was the most common clinical infection. Uganda is in the top 15 TB burden countries globally with a high incidence of HIV-TB co-infection. Children are continually exposed to adults with TB, and those family members are also HIV-infected.
Of the 25 children with mycobacterial-IRIS, 3 (2.1%) had clinical BCG-IRIS with ipsilateral lymphadenopathy with ulceration or abscess formation at the site of the BCG scar at time of the study visit. This has also been described in a South African pediatric cohort of children <24 months with a higher 11.2% prevalence of BCG-IRIS [27
]. In restricting our cohort to children <12 months, the prevalence of BCG-IRIS was 19% at time of the study visit. The overall incidence may have been higher.
Little information exists on how ART affects the course of dermatologic conditions in children whereas in adults dermatological manifestations of IRIS appear to be the most frequent [17
]. This study has demonstrated that dermatological manifestations were the most common IRIS events. Some of the types of dermatologic events have been reported in adults [7
], such as paradoxical Kaposi sarcoma, molluscum contagiosum, and varicella zoster.
Other manifestations were considered as unmasking IRIS events due to their unusual, exaggerated presentation. For example, three otitis media episodes presented with exaggerated purulent discharge in conjunction with immunologic success and viral suppression.
This vast clinical manifestation of IRIS depends on the prevailing infections in the locality of HIV-care. Our study was interested in all manifestations of IRIS, thus the diverse presentations observed. In resource-limited areas where screening for OIs is primarily clinical, unmasking of subclinical OIs appears to be common.
Factors associated with IRIS
We did not find that the type of ART regimen, pre-ART Hgb level, CD4+
ratio, previous OI, WHO stage III and IV, a shorter interval between initiating treatment for OI and starting ART, nor a rapid viral load decline to be associated with IRIS, as has been described in other adult cohorts [6
The absolute CD8+
cells at interview <1000 cells/µL was associated with a 4-fold risk of IRIS development. In a U.S. study of 120 adolescents, decreased CD8+
was associated with a temporary clinical deterioration while on ART [29
]. In our population having a low CD8+
T-count correlated with older age.
There is no validated pediatric IRIS case definition to date, and this creates a challenge in diagnosing IRIS. This study used a prospective case definition in conjunction with expert opinion, similar to other recent studies [17
]. Additionally, what is and is not “IRIS” remains controversial in the absence of a gold standard; however the adverse clinical events, whether labeled as IRIS or not, appear to be common in this multi-centered prospective study. We believe these results are generalizable to other Sub-Saharan pediatric populations presenting with advanced AIDS. The clinical implication is that pediatric HIV providers need to be aware of the frequent unmasking of subclinical and previously latent OIs within the first few months of initiating ART.
The design of the study was cross-sectional, thus IRIS events occurring prior to or after the study visit were not included. As such, the total incidence of IRIS cannot be estimated. A future prospective pediatric cohort study is needed in Sub-Saharan Africa to better inform pediatric HIV care. Extrapolating solely from adult cohort studies on the incidence, risk factors, and pathogenesis of IRIS is unwise and may lead to incorrect assumptions regarding pediatric HIV-infected populations.
First, the prevalence of pediatric unmasking IRIS in this study was high and is likely to continue for the foreseeable future in the resource-limited countries as long as HIV maternal-to-child-transmission (MTCT) continues unabated coupled with children presenting late for HIV-care with unknown, advanced immunosuppression. Second, there is need for rapid and early pediatric HIV diagnosis so as to facilitate early ART initiation in order to minimize the HIV-related morbidity and mortality [31
], to which in part IRIS contributes. Third, there is need to reemphasis vigorous TB screening to minimize unmasking of ART-associated TB as this was the most common unmasked clinical infection. Fourth, providers should be aware of the frequent unmasking of subclinical infections in the first few months of ART and counsel caregivers. Finally, improved implementation of MTCT services is needed as a public health strategy to prevent IRIS through eradication of pediatric HIV.