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Smoking cannabis is an independent risk factor for lung disease in people with HIV

Frequent cannabis
smoking is a risk factor for lung disease in HIV-positive men, according to US
research published in EClinicalMedicine.
Smoking cannabis increased the risk of pulmonary diseases – especially those
with an infectious cause – independent of smoking and CD4 cell count. The
research involved approximately 2500 men who have sex with men (MSM), half of
whom were HIV positive. No independent associations were detected between
smoking cannabis and lung disease in HIV-negative men, showing that HIV-positive
individuals are especially vulnerable to lung disease caused by smoking the

“To our knowledge,
this study is the largest investigation of smoked marijuana [cannabis] and
pulmonary diagnoses in HIV infected individuals to date,” comment the authors.
“Current daily or weekly marijuana smoking was associated with elevated risk of
infectious pulmonary diagnoses in HIV+ participants….current marijuana smoking
was also associated with increased risk of chronic bronchitis.”

The authors
believe their findings are of relevance to the care of people with HIV and
that addressing smoked cannabis use could help reduce rates of pulmonary

It is well known
that people with HIV have an increased risk of lung disease. This is partly
because of the high rates of smoking among HIV-positive individuals. However, the
damage caused by HIV infection and immune suppression are also important causes.

Research involving
HIV-negative people has shown that smoking cannabis is a risk factor for
respiratory symptoms such as cough and wheezing, as well as chronic obstructive
pulmonary disease (COPD) and emphysema. However,
relatively little is known about cannabis smoking as a risk factor for pulmonary
disease in people with HIV. 

Investigators form
the ongoing Multicenter AIDS Cohort Study (MACS) therefore designed a study comparing
incidence of infectious lung diseases (such as pneumonia) and non-infectious
pulmonary disease, especially bronchitis, between HIV-positive and HIV-negative
gay and other MSM, after taking into account smoking of cannabis. Analyses also
considered other risk factors for lung disease, especially tobacco smoking, and for people with HIV,
CD4 cell count.

The study
population consisted of 2704 men aged 30 years and older. Half were
HIV positive. Participants were recruited between 1996 (the year combination antiretroviral therapy (ART) was first introduced) and 2014. The average duration of follow-up was a
little over ten years. Participants were asked about the frequency and
intensity of smoking of cannabis and tobacco, as well as lung disease diagnoses (the
latter were also verified using medical records).

The participants
had a median age of 44 years and over two-thirds were white. The majority (90%) of HIV-positive people were taking ART and 60% had a CD4 cell count above 350 cells/mm3.

Weekly or daily
cannabis smoking lasting at least one year was reported by 27% of HIV-positive
individuals and by 18% of HIV-negative individuals. Median duration of
daily/weekly cannabis smoking was approximately four years for both groups.

A history of smoking
tobacco was a little more common among individuals with HIV compared to those who were
HIV negative (65% vs 61%).

Rates of lung
disease due to infectious causes were significantly higher among HIV-positive
people than HIV-negative study participants (33% vs 22%).

The same was also
true for non-infectious lung disease (21% vs 17%).

Closer analysis
showed that in people with HIV, rates of both infectious and non-infectious
lung disease were markedly higher among cannabis smokers than non-cannabis smokers
(41% vs 30%; 25% vs 19%). This finding was not replicated in the HIV-negative
group (24% vs 21%; 15% vs 18%).

In HIV-positive
participants, the strongest risk factor for diagnosis with a pulmonary
infection was a CD4 cell count below 200 cells/mm3 (aHR =3.37; 95%
CI, 2.58-4.41, p < 0.001). Current
daily or weekly cannabis smoking was also a significant risk factor (aHR =
1.34; 95% CI, 1.06-1.71, p = 0.016).

After taking into account CD4 cell count
and smoking status, recent daily or current cannabis use increased the risk of
diagnosis with an infectious lung disease by 48% (aHR = 1.48; CI: 1.05-1.75, p = 0.035)
with long-term use over two years increasing the risk by 10% (CI: 1.04-1.16, p
= 0.012). These risks were amplified by tobacco smoking.

No association was
found between smoking cannabis and infectious pulmonary disease among the
HIV-negative participants.

Turning to non-infectious lung disease, though both low
CD4 cell count and cigarette smoking were stronger risk factors, current
cannabis smoking was also a risk factor for the development of chronic bronchitis among men with HIV (HR = 1.54; 95% CI, 1.11-2.13, p = 0.0093).
There was no significant association between smoking cannabis and non-infectious
pulmonary disease in HIV-negative individuals.

“These findings
confirm the known association between HIV infection and increased prevalence of
pulmonary disease, and provide evidence that HIV-infected individuals may be
more vulnerable to marijuana’s effects on lung disease compared to uninfected
participants with similar exposures,” note the authors.

The effect of
daily or weekly cannabis smoking on infectious lung disease risk among people with HIV was equivalent to that associated with smoking ten cigarettes daily.

“Marijuana smoking
is a modifiable risk factor that healthcare providers should consider when
seeking to prevent or treat lung disease in people infected with HIV,
particularly those with other known risk factors,” conclude the authors. “Given
increased trends of regular marijuana smoking among HIV-infected people…more
studies are needed to evaluate potential merits of non-smoked rather than
smoked forms of marijuana for medicinal and other purposes.”

Full story is available here.

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