by Janelle Weaver

The combination of air pollution and HIV infection may have a greater detrimental impact on the cognitive abilities of school-aged children than exposure to either factor alone, according to an NIEHS-funded study. The findings, published in January 2018 in the International Journal of Environmental Research and Public Health, also reveal an alarmingly high prevalence of air pollution exposure, regardless of HIV status, in children living in urban settings in Sub-Saharan Africa.

“Our findings suggest that HIV-infected children may be particularly vulnerable to the detrimental impact of environmental neurotoxicants,” said senior study author Sarah Benki-Nugent, Ph.D., a clinical assistant professor of global health at the University of Washington School of Public Health. “Our ultimate goal is to use this information to develop strategies to reduce exposures during critical periods of brain development and improve long-term cognitive outcomes in these vulnerable children.”

The majority of all HIV-infected children under 15 years of age live in Sub-Saharan Africa, where air pollution is also a major public health concern. A growing body of evidence suggests that HIV infection and chronic exposure to air pollution in early life can each impair cognitive abilities by causing neuronal dysfunction and cell death. But until now, it was not clear whether these two factors interact to further worsen neurocognitive function. Moreover, relatively little is known about the impact of air pollution on child health and developmental outcomes in Sub-Saharan Africa, particularly in dense urban settings such as Nairobi, Kenya.

To address these questions, Benki-Nugent and her team recruited 49 HIV-uninfected and 45 HIV-infected children who resided in Nairobi and ranged in age from five to 12 years. The researchers assessed their exposure to carbon monoxide using air monitors worn by caregivers and hung over cooking stoves for a 24-hour period. They also collected the children’s urine samples to measure 1-hydroxypyrene (1-OHP), a key metabolite of environmental pollutants called polycyclic aromatic hydrocarbons. In addition, a detailed battery of tests was used to evaluate the neurocognitive functioning of the children.

After adjusting for child age and household monthly rent, higher 1-OHP levels were associated with worse scores for memory, attention, and global cognitive ability in HIV-infected children, but not in HIV-uninfected children. Statistical tests confirmed a significant interaction between the two factors, that is, the combined effect of HIV infection and air pollution exposure on memory and attention was greater than the estimated sum of their individual effects. There was also a significant interaction between caregiver carbon monoxide levels and HIV infection for attention.

“The susceptibility among HIV-infected children, but not uninfected children, is a novel and important observation,” said Claudia Thompson, Ph.D., the branch chief for the Susceptibility and Population Health Branch at the NIEHS. “Given the large global population of children co-exposed to higher levels of air pollution and HIV in Sub-Saharan Africa, continued emphasis on characterizing and reducing risk factors for poorer neurocognitive health in the HIV-infected population is merited.”

Regardless of HIV status, approximately 41% of the children were exposed to carbon monoxide levels above the World Health Organization (WHO) threshold, and 1-OHP levels were similar to those of U.S. smokers. “The high levels of air pollution observed in our study underscore the need to further understand the health impacts of these exposures, and whether interventions to decrease exposure to combustion byproducts can provide benefit,” said first author Megan Suter, a doctoral student in epidemiology at the University of Washington School of Public Health.

In the future, Benki-Nugent and her team plan to carry out a more comprehensive evaluation of environmental exposures in HIV-affected households. “We hope to use this information to develop low resource-appropriate tools to reduce pollutant exposures,” she said. “Taking a multifaceted interventional approach—combining biomedical interventions like antiretroviral therapy with interventions to improve indoor air pollution—may be necessary to optimize neurocognitive outcomes for children with HIV in regions with high air pollution exposures.”

Read the National Institute of Environmental Health Sciences story

Citation: Suter MK, Karr CJ, John-Stewart GC, Gómez LA, Moraa H, Nyatika D, Wamalwa D, Paulsen M, Simpson CD, Ghodsian N, Boivin MJ, Bangirana P, Benki-Nugent S. 2018. Implications of combined exposure to household air pollution and HIV on neurocognition in children. Int J Environ Res Public Health. 2018 Jan 20;15(1). pii: E163. doi: 10.3390/ijerph15010163. [Abstract]