Global health: infectious disease and AIDS: history and progression Flashcards
When do we think the first case of HIV occurred in the UK
Manchester, 1959.
What was the significance of the post mortem
The post mortem showed:
Pneumocystis carinii pneumonia (PCP)
cytomegalovirus (CMV) infection
These conditions had never been previously reported in adults
The case was reported as a rare condition and never referred to for more than 20 years
What was HIV first referred to as
By April 1981 the doctor had seen 5 men with a similar illness.
They were all in their early 30s, white and gay.
By June a report was published about this curious new health problem among homosexual men
What is the point of epidemiology
To track the presence of new diseases
What is the purpose of Centre of Disease and Control
Way of reporting notifiable diseases, centralised reporting system, allows us to evaluate the scale of the problem.
What was the initial hypothesis for patients with GRID
An environmental factor? bad batch of drugs inhaled nitrates (poppers) An infectious disease a new virus a strange combination of existing agents
What is meant by case collecting
Go round hospitals asking healthcare professionals whether they have seen patients that fit their criteria, allows us to monitor its progress and potentially its cause.
How many people had HIV in the USA in 2006
1.3 million
What are some of the factors for HIV
Male-to-male sexual contact
Intravenous drug use
Male-to-male sexual contact and IDU
High risk heterosexual contact.
What is meant by the case
A person living with said condition.
How do we perform a case-control study
Identify cohort of cases, and cohort of people without the case.
Try to identify what is different, which may indicate to what is causing the disease.
What did the initial case-control study with HIV show
75% of living cases were interviewed, along with controls for each patient
Asked about all possible exposures
sexual, medical, chemicals, pets, plants….
Results
Cases had twice as many sexual partners, and partners also had more partners
Cases had more history of syphilis
No association with “poppers”
The only main common factor was the disease was seen amongst young gay men and seemed to be related to sexual contact with each other- called CASE CLUSTERING- suggesting infectious agents
It was called GRID- Gay related Immune deficiency
What is meant by a case-control study
A case control studies sets out a known outcome and compares individuals with or without this outcome and determines what connects them. e.g. post op infections over a given time of an outbreak cases: knee op with infection controls knee op no infection. They are retrospective.
How do we design a case-control study
a case-control study is always retrospective because it starts with an outcome then traces back to investigate exposures. A case-control study is designed to help determine if an exposure is associated with an outcome (i.e., disease or condition of interest).
First, identify the cases (a group known to have the outcome) and the controls (a group known to be free of the outcome). Then, look back in time to learn which subjects in each group had the exposure(s), comparing the frequency of the exposure in the case group to the control group.
What are the advantages of case-control studies
cheap, quick, good for investigating outbreaks fo infectious diseases. Ideal to study RARE disease. Possibility to collect detailed clinical history.
What are the disadvantages of case-control studies
o Possible bias in control selection. o Bias in exposure assessment (e.g. recall bias). o Uncertainty in exposure to disease temporal relationship. o Cannot estimate disease incidence.
Describe the clustering of cases in HIV
Clustering of cases
Bill Darrow
“It looks more like a sexually transmitted disease than syphilis”
BUT then not all cases were amongst gay men:
Cases in injecting drug users & transfusion/Factor VIII recipients
10 women with the disease, all had sex with bisexual men or drug users
Describe the detective work involved in HIV
A number of early patients happened to mention being friends with an air steward from Canada
Investigators asked patients to name all their sexual partners
Nine of first 19 cases in Los Angeles were sexually linked to the airline steward
Several gay men presenting with sickness were or had been sexual partners
Apparent long incubation period
Describe the evidence linked with HIV
Cases with clear source of infection
monogamous sexual partners of affected people
babies transfused at birth
Haemophiliacs received contaminated blood products
Finding the virus - 1983
Testing for the virus - 1984- TAKES TIME TO DEVELOP WIDEPREAD ACCURATE TESTS
retrospective testing of stored sera
1978 <1% positive
1980 20% positive
NO TREATMENT
How is HIV transmitted
Transmission through body fluids: sexual contact , breast feeding or blood
Where does the majority of the burden of HIV lie
90% of disease in developing countries
Define prevalence
The frequency of a disease in a population at a point in time
= number of cases in population
number of people in population
What is prevalence used for
Prevalence measures burden of disease in a population
It is useful for planning
It can be used to compare burden of chronic disease between populations
How many people are currently living with HIV
36.9 million [31.1 million–43.9 million] people globally were living with HIV in 2017.
What is the mortality of HIV/AIDS
1 million deaths a year
Define incidence
The number of new infections within a population over time within a certain defined population.
Usually defined annually.
How do we reduce prevalence
By reducing incidence- hasn’t been reduced much worldwide, but UK is seeing larger reductions.
Where are the majority of new diagnoses of HIV in the UK from
the UK, we are lacking a prevention strategy.
What is the key target for WHO
No new infections
No new babies infected- ONLY CUBA has achieved this, universal screening, prevention given to those infected.
No more HIV related deaths globally
How do we estimate incidence
Need to define the time period under question
Need to define the denominator; what is the total population at risk; for this example it is all the people living in Sierra Leone during this time period
Need an accurate test to define a true case; a blood test for Ebola is either positive or negative and if it was newly positive this suggests a new case or incident infection. This is easy to do for infections that have a short time period but what for chronic infections eg HIV where a positive antibody test does not always mean it is a new infection ?
How can incidence influence policy
in the case of Ebola once incidence has reached near zero we declare the outbreak over and can reopen schools etc
Define mortality
Number of deaths from a disease in a population over a given time (usually annually).
= Deaths from disease in a given time period
population at start of time period
How many people died from AIDS in 2017
940 000 [670 000–1.3 million] people died from AIDS-related illnesses in 2017.
When is the epidemic stable
If mortality = incidence the epidemic is stable
The burden globally is the same
How can prevalence increase, even if mortality decreases
If we keep more people alive with ART then the mortality reduces and potentially people are alive longer
As mortality goes down more people are alive and live longer they can:
transmit virus to sexual partners and their babies and incidence may go up
prevalence increases as more cases are transmitted as well as people not dying
Need to reduce incidence,
Explain the relationship between mortality and prevalence
Define prevalence and mortality
For diseases where treatment confers survival benefit (eg ART for people living with HIV) the mortality falls as people start ART. Hence these people survive and overall population level prevalence increases.
For diseases that are rapidly fatal (eg Ebola) the mortality is rapid and high and so large number of cases but overall prevalence is low.
What do prevention tools depend on
How the disease spreads, and life span of person infected with that pathogen.
How can we explain that as prevalence increases incidence can reduce in the setting of HIV infection?
Antiretroviral therapy (ART) improves survival of people living with HIV as more people living with HIV receive ART (15 million people globally are on ART) the prevalence of HIV within a population increases. ART also reduces the risk of onward viral transmission by limiting the level of virus in the blood and secretions of people living with HIV to almost zero (HPTN052, PARTNER study, PMTCT studies). Therefore the more people taking ART the less people within a population transmit infection and so incidence reduces.
What were the objectives of IAS 2010
i) Recognize and use HIV treatment as a tool for preventing new infections
ii) Develop better combination antiretroviral medications and cheaper diagnostics tools
iii) Find ways to lower other HIV-related costs
iv) Expand the availability of HIV testing and build stronger links between HIV testing and care
v) Encourage and support community leadership in expanding and improving local HIV responses.
Why may people not take HIV tests
Stigma, issues with obtaining ART- human nature interferes with our ability to get to zero.
What does risk of passing HIV onto sexual partner depend on
Viral load
Where are the gaps in HIV treatment
Young men and women
Migrants
People not linked into care, and with transient sexual partners.
What are the 6 leading causes of deaths in low income countries
Lower Respiratory tract infection Diarrhoea HIV/AIDS Ischaemic heart disease Malaria Stroke CVD TB
What were the top 10 global causes of death in 2016
Ischaemic heart disease
Stroke
COPD
Lower Respiratory tract infections Alzheimer disease and other dementias Trachea, bronchus, lung cancers Diabetes mellitus Road injury Diarrhoeal diseases TB
What are the 6 leading causes of deaths due to infectious disease
- Lower respiratory Tract infections Liam 2. HIV/AIDS Had 3. Diarrhoeal Diseases Diarrhoea 4. TB That 5. Malaria Made 6. Measles
