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evolving Western blot test, and subsequent
demonstration of full antibody seroconversion.
Seroconversion typically occurs within 21-28 days after exposure (range 7 days to 12
months). The classic presentation of acute retroviral syndrome resembles a mononucleosis-like illness,
which is often mistaken for malaria in tropical settings. The most common symptoms include fever,
fatigue, myalgia/arthralgia, pharyngitis, lymphadenopathy, rash, anorexia, non-specific gastrointestinal
complaints, and sometimes neurological symptoms. Symptoms spontaneously resolve in most patients.
There is evidence that the persistence of the acute retroviral syndrome beyond 14 days, as well as a
shorter incubation than 21 days, are predictors of a more rapid progression to AIDS. Significant viraemia
persists for several weeks, and subsides after 9-12 weeks to much lower levels, while at the same time the
ICAO Preliminary Unedited Version — November 2009 III-13-3
level of CD4+ T cells increases after having reached its trough at about 6 weeks after infection (Fig. 1).
During the period of peak viraemia, it is believed that HIV-specific immune responses begin to drive
down the viral load until a “set point” between viral replication and immune pressure is reached. This
occurs within the first 6-12 months following infection, and most HIV-researchers assume that the level
of this set point is highly prognostic of the patient’s rate of progression to AIDS.
Once the infection has been established, the virus is never cleared completely from the body. A chronic
infection develops that persists with varying degrees of virus replication. For adults in developed
countries, the average time of progression to the clinical signs and symptoms of AIDS is approximately
10 years in the absence of antiretroviral therapy. Progression is markedly age-related, with older patients
doing much worse than younger patients. Although the patients are asymptomatic during this period, in
the majority of untreated cases viral load gradually increases and CD4+ T cells gradually decrease,
patients become symptomatic and clinically ill finally developing severe opportunistic infections. Some
(20 per cent) untreated persons develop AIDS defining illnesses within 5 years of infection, whereas
others (<5 per cent) have sustained long-term (>10 years) asymptomatic HIV infection without decline of
CD4+ T cell counts to <500/μL. Perhaps 2 per cent of untreated infected persons – often called
“long-term non-progressors” – seem to be able to contain HIV replication to extremely low levels and
maintain stable CD4+ T cell counts within normal range for lengthy periods (>12 years). The appearance
of effective antiretroviral therapy, resulting in near-complete suppression of viral replication, has brought
long-term delay of progression to AIDS-defining illnesses and prevention of related conditions for many
HIV-seropositive subjects in the developed world. These medicines also appear to significantly reduce the
rate of sexual and vertical transmission of the virus and are of importance in a population such as aircrew,
who are highly mobile.
CLINICAL MANIFESTATIONS OF HIV INFECTION
The latency period (clinical latency period; Fig. 1) is characterized by large inter-individual variability in
duration. Initial symptoms of HIV-related immunosuppression (Stage 2, mild symptom, in the WHO
clinical staging classification) include herpes zoster, recurrent upper respiratory tract infections (UTRIs)
and seborrhoeic dermatitis. Stage 3 denotes more advanced symptoms and includes persistent oral
candidiasis, oral hairy leukoplakia, severe weight loss or fever or chronic diarrhoea and severe bacterial
infections or pulmonary tuberculosis.
After a latency period, untreated HIV-positive individuals will develop WHO Stage 4 disease or AIDSdefining
illnesses, which may be characterized by neuropsychiatric symptoms including dementia,
cognitive or other psychological changes associated with HIV encephalopathy, opportunistic respiratory
and central nervous system (CNS) infections, and diseases of the cardiovascular, gastrointestinal,
hepatobiliary, renal, genitourinary, and endocrine system. The majority of neurological disorders will be
HIV-associated dementia complex (HAD). Other neurological involvement includes myelopathies,
peripheral neuropathies and myopathies, opportunistic infections, primary central nervous system
lymphoma, and cerebrovascular diseases. Moreover, cognitive and psychiatric symptoms, visual changes,
headache, seizures, dizziness, involuntary movements, gait disturbances, cranial neuropathies and focal
deficits can impair safe functioning of HIV-positive personnel engaged in aviation duties. Conditions
　
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