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tests (two standard deviations) is defined approximately as more than a 30 per cent change of the
count. For practical use, a decline in CD4+ T cells by 75/year is considered to indicate a higher
risk for progression to AIDS, when the reference CD4+ T cell count is <500/μL. A CD4+ T cell
count of <200/μL is AIDS-defining even in the absence of any signs and symptoms of HIV
disease.
Viral load.— The rate of progression of HIV disease is predicted by the magnitude of active HIV
replication, which is reflected by the viral load. Measurement of the viral load through the use of
quantitative plasma HIV RNA assays permits estimation of the relative risk of disease
progression and time to death. However, plasma HIV RNA levels obtained within the first six
months of HIV infection do not accurately predict disease progression. In contrast, plasma HIV
RNA levels stabilize after approximately six to nine months of initial HIV infection, and the viral
set point is considered predictive of subsequent disease progression. Immunizations and
intercurrent infections can lead to transient elevations of plasma HIV RNA levels. Values
ICAO Preliminary Unedited Version — November 2009 III-13-6
obtained within four weeks of such episodes may not accurately reflect the actual plasma HIV
RNA level. Two specimens should be obtained within one to two weeks of each other and
analyzed by the same quantitative method (either Branched DNA=bDNA, or Reverse
Transcriptase Polymerase Chain Reaction = RT-PCR). Plasma HIV RNA assays are also used as
the best measure of the activity of antiretroviral therapy. A viral load of <5000 copies/mL is
considered low and provides evidence for non-progression of the disease. The minimal change in
viral load considered to be statistically significant (2 standard deviations) is a threefold or a 0.5
log10 copies/mL change. For practical use, an increase by >20,000 copies/year is considered to
indicate a higher risk of progression to AIDS.
b) Evaluating co-infection
Hepatitis B and C are frequent co-infections in HIV-infected individuals. They can cause
progressive liver disease especially in those receiving anti-retroviral therapy. The progression of
HIV infection appears to be slowed in people co-infected with Hepatitis G virus. Other sexually
transmitted diseases such as syphilis should also be considered. Tuberculosis is the most common
HIV associated opportunistic infection in developing countries, compared to pneumocystis
pneumonia in industrialised countries. Cytomegalovirus is the most frequent cause of retinitis in
advanced HIV infection. Other associated co-infections include Epstein-Barr virus, toxoplasma
gondii (associated with multiple CNS lesions) and JC virus (named after the initials of the patient
in whom it was first discovered) that cause progressive multifocal leukoencephalopathy, and
cryptococcal meningitis, particularly in tropical countries.
c) Neurological evaluation
The spread of HIV-1 into the CNS is known to occur early in the course of the infection.
However, except for early HIV-associated meningitis (as part of an acute HIV seroconversion
illness), the majority of nervous system complications of HIV in the CNS take years to appear.
HIV-related neurological disorders may arise from infection, neoplasm, systemic metabolic
derangement, antiretroviral therapy, or direct HIV effects on the nervous system.
Several large-scale studies have shown that HIV-associated cognitive dysfunction is antedated by
immunological (CD4+ T cell) decline. This finding is important when considering aeromedical
fitness.
During neurological examination, specific attention should be paid to extra-pyramidal signs, and
ocular disorders such as dissociated nystagmus, gaze-evoked nystagmus, impaired saccadic
function, and smooth pursuit. Testing of primitive reflexes (glabellar, snout, Rossolimo1, digital
signs) should be part of the examination because they are associated with cognitive decline in
HIV patients without overt neurological disease.
Most studies demonstrate that the risk of new-onset seizures in asymptomatic individuals is low.
In the majority of cases, seizures in HIV-positive individuals are caused by disorders that
generally occur in late stages of HIV-infection, such as encephalopathy, neoplasm, or
opportunistic infections.
1 Rossolimo’s reflex: Percussion of the plantar surface of the 2nd to 5th toes causes flexion which is
exaggerated greatly in pyramidal tract lesions. After Grigorii Ivanovich Rossolimo, Russian neurologist,
(1860-1928).
ICAO Preliminary Unedited Version — November 2009 III-13-7
d) Cognitive function testing
HIV associated dementia (HAD), also known as AIDS dementia complex and HIV
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Manual of Civil Aviation Medicine 2(93)
