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Category: Infectious Diseases

Two types of tests for SARS-CoV-2 currently predominate. The first are molecular tests, based on PCR technology, that detect the presence of viral nucleic acid and therefore indicate a current infection. The second are serology tests that are designed to detect anti-SARS-CoV-2 antibodies (usually IgG) generated by the immune systems of individuals who have been infected in the past.

RT-PCR to detect SARS-CoV-2 virus is relatively slow and requires specialist laboratories. At the outset of the pandemic, testing capacity was too low to meet the needs of governments, and even 6 months later demand for tests can outstrip supply in areas where there is a surge of infections. At the end of June 2020 Quest Diagnostics, a key player in COVID-19 testing in the USA, announced that only the highest risk patients could get a test result faster than 3-5 days. Other companies reported similar issues.

Alternatives to slow and expensive procedures such as RT-PCR testing do exist. Rapid tests based on Lateral Flow technology have been put forward as a faster, cheaper, low technology alternative to RT-PCR testing. However, this technology is fundamentally of lower sensitivity than PCR-based testing; while PCR is able to exponentially increase the signal until it is detectable, Lateral Flow (also known as immunochromatography) tests have little scope for signal amplification.

An example of Lateral Flow rapid tests

There is also the question of what tissue type to use for the testing. While many rapid tests use serum or plasma derived from blood as the sample of choice, that would only be a suitable matrix for SARS-CoV-2 testing if the virus was present in samples from infected individuals. In the case of SARS-CoV-2 it would seem that blood (and therefore serum and plasma) is not suitable. In a March 2020 JAMA paper, Wang et al. reported that using RT-PCR, SARS-CoV-2 was only identified in 3 out of 307 blood samples (1%) collected from up to 205 patients in China.

Since the virus is thought to be spread by droplets in coughing and sneezing, saliva has been considered a high potential sample type for rapid tests. It does seem that in many cases the virus is present in saliva samples – a recent paper by Azzie et al. in the Journal of Infection has determined that in a cohort of 25 patients with severe COVID-19, virus was detectable in the saliva of all 25 of them via RT-PCR. The Cycle Threshold values ranged from 18 to 32 with a mean average of 27. The extent to which the virus is present in asymptomatic patients remains to be determined.

A further challenge around rapid antigen detection in saliva or other sample types is sensitivity. RT-PCR is highly sensitive and theoretically able to detect a very low number of viruses. However, in a recent study by Mizuno et al. on >100 patients, virus was only detected in 11.7% of them using a rapid antigen test (Fujirebio) compared to up to 82% using molecular diagnostic tests.

Intriguingly, faeces and rectal swabs have a high potential as a positive sample type; in a review article Bwire et al. reported positive rates of 32.8% and 87.8%, respectively. Rectal swabs have a vastly superior positive rate according to this review than both nasopharyngeal (45.5%) and oropharyngeal (7.6%) swabs. Although they are perhaps not so amenable to drive-through testing(!), they have some potential for self-testing at home.

Our surprising conclusion is that stool samples may be the best matrix for rapid SARS-CoV-2 virus testing. Serum and plasma are clearly not suitable and saliva, which is perhaps the most convenient alternative, may have a lower viral load than stools. A further challenge with both stools and saliva is that they are likely to need diluting into a suitable liquid prior to testing, to enable them to flow down the test strip. This would reduce the test sensitivity even further .

If rapid tests cannot reach the levels of sensitivity of RT-PCR tests, do they have any utility? Some believe that they do. If it was possible to make such a cheap and easy test that everyone in the country could be tested, say, 1 or 2 times every day, it could be that at some point in the infection cycle those carrying infections would have a high enough viral load to test positive using a low sensitivity test. In the context of this pandemic where a large proportion of those infected never find out due to being asymptomatic or not ill enough to get tested, this may be of value, and is presumably why companies continue to pursue the holy grail of SARS-CoV-2 rapid testing.

Logical Biological provides human patient material for SARS-CoV-2 relevant to both virus and serology testing. This includes nasal swabs with quantitative PCR results, saliva and serum/plasma.

Blog Overview

August 5th 2020
Antigens Immunoassays Infectious Diseases Saliva Swabs
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We are in the midst of the most significant global pandemic since the 1918-19 Influenza pandemic, over 100 years ago. The 2020 pandemic has been caused by a Coronavirus, named SARS-CoV-2, which confers a severe respiratory illness (COVID-19) on a proportion of those infected. The virus is readily transmissible from human to human with many of those infected showing no or mild symptoms, meaning it is hard to know who has been infected.

The virus has resulted in severe economic impacts because many countries have adopted “lockdown” policies in order to limit its spread by limiting interaction between individuals. One idea for mitigating some of the economic impact has been to identify and liberate from lockdown those individuals who have already been infected by the virus and may therefore be immune from future infections. As yet, it is not known for sure if previous infection by the virus renders individuals immune from future viral challenge, nor how long such immunity would last for. However, for this idea to be viable, diagnostic tests that can identify the SARS-CoV-2 antibodies in the human blood are required. Such tests have been made by innumerable manufacturers but they vary greatly in their performance.

 

At what stage are antibodies exhibited?

To understand the value of SARS-CoV-2 antibody tests we need to know who exhibits what antibodies, and when. It is assumed that the vast majority of individuals will have a detectable antibody response, regardless of whether or not they are symptomatic. The below data suggests IgG and IgM antibodies are detectable 1-3 weeks after SARS-CoV-2 symptom onset.


Detection of IgG, IgM and Neutralising (NT) antibodies over time since symptom onset.
Taken from a pre-print published online by Borremans et al., (2020)

 

Why 100% test specificity is essential for SARS-CoV-2

Logical Biological received some CE-marked SARS-CoV-2 IgG and IgM antibody tests a few weeks ago (we won’t name the manufacturer). In the pack insert these tests reported 97% specificity, which sounds high, but what does it mean in the context of the proportion of people who actually have been infected in the population? Specificity can be defined as the number of true negative cases that actually return a negative test result.

As can be seen in the tables below, if 1 person is selected at random and tests positive using a 97% specificity test when the prevalence within the population is low, it is much more likely that a positive test result is a false positive than a true positive.

Even with a 99.6% specificity test, such as those now available in a leading UK high street pharmacist, there is a clear threat of false positives, the proportion of false positives to actual positives reducing as the true number of infected within the population increases. One serology study, performed in Santa Clara, California, received criticism that the specificity of the test was too low, at only 99.5%. Only with 100% can we be fully confident that the positive test result is a true positive. Fortunately, such tests are now becoming available, such as one developed by Ortho Clinical Diagnostics.

The tables below consider a random selection of the population. Individuals may feel more confident about a positive result they receive if they have also shown the classical symptoms.

97% Specificity

% of population prev. infected Test Specificity True positives (per 1000) Expected False positives (per 1000)
0.1% 97.0% 1 30
1% 97.0% 10 30
10% 97.0% 100 30
100% 97.0% 1000 30

 

99.6% Specificity

% of population prev. infected Test Specificity True positives (per 1000) Expected False positives (per 1000)
0.1% 99.6% 1 4
1% 99.6% 10 4
10% 99.6% 100 4
100% 99.6% 1000 4

 

100% Specificity

% of population prev. infected Test Specificity True positives (per 1000) Expected False positives (per 1000)
0.1% 100.0% 1 0
1% 100.0% 10 0
10% 100.0% 100 0
100% 100.0% 1000 0

 

Sensitivity

Sensitivity of a test can be defined as the proportion of those genuinely bearing a marker (such as SARS-CoV-2 antibodies) who test positive for it. In the context of SARS-CoV-2 antibody tests, results from low sensitivity tests are less “dangerous” than results from low specificity tests. Low specificity tests could result in a situation where susceptible individuals who have wrongly tested positive, believing themselves to be both immune and non-infective, stop taking precautions to protect themselves and others, leading to further infections. On the other hand, low sensitivity tests would likely result in previously-infected individuals who have wrongly tested negative continuing to be cautious and since they have already had the infection would not be able to contribute to further spread in any case.


Table shows theoretical results of a 97% sensitivity test

% of population prev. infected Test sensitivity True positives (per 1000) Expected positives based on 97% sensitivity
0.1% 97.0% 1 0.97
1% 97.0% 10 9.7
10% 97.0% 100 97
100% 97.0% 1000 970

 

 

How many people have actually been infected by SARS-CoV-2?

One of the countries most affected by the pandemic has been Spain. The government of Spain has recently performed a serological study (results published on 13th May 2020) where they assessed the blood of 70,000 individuals. The most affected province showed 14.2% positive tests whereas the least affected regions were at less than 2%. The overall figure for previously-infected individuals in Spain was assessed to be approximately 5%. The test looked for both IgG and IgM antibodies. In the context of the above information, it should be noted that the test used was reported to show 100% specificity and 79% sensitivity for IgG. This means it would miss 21% of those previously infected and also may miss some people in the early stages of infection. It was wise of them to choose a 100% specificity test, and in the context of a serological survey to assess prevalence within a large population, the results can be adjusted to account for the low sensitivity of the test.

Data from other countries is in line with that from the Spanish study. For example, study results announced on April 23rd from another of the world’s major hotspots, New York State, USA, found 21% of people to be antibody positive in New York City. High figures (10-20%) were also seen in other areas while outside of the most-affected areas in the state the average prevalence was 3.6%.

 

Conclusion

The prevalence of SARS-CoV-2 in some locales is 2-20%. At the upper end of this range the % of positive tests that would be false when using a 97% specificity test would be significant and unacceptably high. At the low end of this range there would be more false positives returned than true positives, rendering such a test completely useless. Beware SARS-CoV-2 antibody tests with <100% specificity.

 

Available from Logical Biological

  • SARS-CoV-2 PCR positive serum/plasma/swabs
  • SARS-CoV-2 IgG positive serum/plasma – 1ml samples and bulk units
  • SARS-CoV-2 IgM positive serum/plasma – 1ml samples and bulk units
  • Pre-Covid19 serum/plasma from normal healthy donors – any quantity

Due to the dynamic nature of the SARS-CoV-2 pandemic this blog post will be out of date shortly after it is written.

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May 27th 2020
Immunoassays Infectious Diseases
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Lyme disease is an infectious disease caused by Borrelia bacteria transmitted by tick bites from ticks of the Ixodes genus. Particularly if untreated, serious and long-term symptoms can occur such as neurological problems, facial palsy, lower limb impairment, heart complications, arthritis, encephalomyelitis and psychosis. It is estimated to affect 300,000 people per year in North America and 65,000 in Europe. Transmission can occur across the placenta during pregnancy.

The causative agent of Lyme disease is a group of bacteria called Borrelia burgdorferi sensu lato. The group comprises 21 closely related species but only 4 of them clearly cause Lyme disease:

  • B. mayonii
  • B. burgdorferi sensu stricto
  • B. afzelii
  • B. garinii

The incubation period for Lyme is usually 1 to 2 weeks but can be longer or shorter. Most of those infected did not realise they had been bitten by a tick as the causative ticks are very small in the nymphal stage.

You didn’t want to see a picture of a tick, did you?

Some people infected with Lyme develop a distinctive bullseye-shaped rash known as erythema migrans. These are perhaps the lucky ones as the presence of it aids Lyme diagnosis. However, the rash commonly fails to conform to the notion of what it is supposed to look like and this can result in Lyme being misdiagnosed as spider bites, cellulitis or shingles. The rash can even be absent entirely and this makes it particularly challenging to diagnose since the other early symptoms of Lyme disease (fever, fatigue, etc.) are ones which are also common to a multitude of other ailments.















The classic Lyme erythema migrans rash

Aside from the rash, Lyme diagnosis typically looks for the patient’s immune response. Anti-Lyme IgM antibodies can usually be detected at 2-4 weeks post-infection, while Anti-Lyme IgG antibodies are usually present 4-6 weeks post-infection. IgM antibodies diminish approximately 4-6 months after infection while IgG antibodies can persist for years. Confusing the issue, the IgM antibodies can persist for years in some individuals and Lyme IgG may never be produced in some “seronegative” individuals. A seronegative patient who doesn’t get the classic rash – that’s going to be difficult to diagnose.

The reason for IgM antibodies being present in chronic patients could be the bacterium reactivating and producing novel proteins, recognisable to the immune system, due to genome instability in the bacterium. The host’s immune system therefore may recognise the altered bacterium as a new one it hasn’t encountered before and develop IgM antibodies against it.

The US Centers for Disease Control recommends a two-tier protocol – first test with ELISA or Immunofluorescence Assay to detect anti-Lyme antibodies, and if it is positive or equivocal, a Western Blot should be performed, also detecting anti-Lyme antibodies. Since Lyme disease is caused by numerous strains of bacterial species with inherent genome instability, the Western Blot test looks for antibodies raised by the patient against a large number of host proteins. Multiple bands should be present for the test to be considered positive.

Lyme Western Blot result annotated with protein bands and molecular weights

 

 

 

 

 

 

 

 

 

False positives are rare although possible where anti-Lyme antibodies cross-react with other bacterial antigens present in the patient sample, but false negatives are common particularly early in testing, partly because the anti-Lyme antibodies take some time to develop following the infection.

PCR is not particularly useful for Lyme diagnosis because of low sensitivity in certain sample types and a poor ability to detect Borrelia DNA in patients with neuroborreliosis.

If test sensitivity is the ability to correctly identify those with a disease and test specificity is the ability to correctly identify those without the disease, Lyme tests sadly still have some way to go to reach 100% for either metric.

 

Bulk Lyme IgM plasma is available from Logical Biological.

Congratulations! Anyone reading this far qualifies for extra reading.

Extra Reading: The Accuracy of Diagnostic Tests for Lyme Disease in Humans, A Systematic Review and Meta-Analysis of North American Research.
Waddell. L. et al. PLoS One. 2016, 11 (12).

Blog Overview

December 3rd 2019
Immunoassays Infectious Diseases
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Toxoplasma gondii is a protozoan parasite present in a third of the world’s human population. People acquire this infection in three ways: i) inadequately cooked infected meat, particularly pork, ii) unwitting ingestion of oocysts passed in cat feces, which could, for example, occur whilst gardening, and iii) pregnant women passing the infection transplacentally to their unborn fetus – known as Congenital Toxoplasmosis.

In most cases the infection is asymptomatic or presents with mild nonspecific symptoms. However, the infection remains in the host indefinitely, latent in the heart, brain, eye, and muscle tissues. It can reactivate in people with weak immune systems, such as patients with advanced HIV disease or those on immunosuppressive therapy, and can result in life-threatening disease.

Fluffy, but could be harbouring Toxoplasma gondii

Congenital Toxoplasmosis  

Women infected prior to conception rarely pass the parasite on to the fetus, although it can happen in individuals where the Toxoplasma has reactivated due to immunosuppression. However, if newly infected with Toxoplasma during pregnancy there is a 20-50% likelihood of the infection being passed to the unborn fetus. The risk of congenital disease is lowest when the maternal infection occurs in the first trimester of pregnancy but the disease is more severe if acquired in the first trimester.

The consequences of being infected as a fetus can be severe, both in infancy and later in life. The list does not make pleasant reading, and includes:

  • Convulsions
  • Deafness
  • Growth impairment
  • Intracranial calcifications
  • Learning disabilities
  • Mental impairment
  • Microcephaly
  • Visual impairment

If an acute infection is diagnosed during pregnancy, treatment can be given which, although not able to influence the likelihood of in utero transmission, can reduce the likelihood and intensity of the manifestations listed above. Drugs include pyrimethamine and sulfadiazine. Despite efforts to encourage prevention, there are sadly around 3000 cases in the United States alone each year.  Abortion may be considered if infection is thought to have occurred before the 16th week of pregnancy or if the fetus shows evidence of hydrocephalus.

Diagnosis

Typically in infections of any type, the host produces IgM antibodies as an initial response to the infection, and later produces IgG antibodies in larger quantities. IgM levels typically drop following the initial infection, whereas IgG antibodies take longer to appear and persist in large quantities.  

Acute toxoplasmosis diagnosis is made tricky by the fact that presence of anti-Toxoplasma IgM antibodies in the host can persist for several years after the infection. Therefore, presence of IgM antibodies in the host cannot lead to the conclusion that an acute infection is present; a study showed that 36% of IgM-positive patients actually had a chronic infection and not an acute infection. False positive test results for Toxoplasma IgM are also an issue.

Furthermore, presence of Toxoplasma IgG, which would typically suggest an older infection, particularly where IgG levels are high, cannot rule out an acute infection; one study found that only 22% of patients positive for Toxoplasma IgM and Toxoplasma IgG actually had an acute infection.

Host antibody response following Toxoplasma gondii infection

So, how is acute Toxoplasma infection diagnosed in pregnant women? Specialised reference laboratories may be able to narrow the time of infection using a wider battery of tests, including tests to IgA, avidity tests and differential agglutination of the AC and HS antigens. Following this, if it is suspected the infection may be acute, the fetus itself may be tested; this typically involves performing PCR on amniotic fluid. Where there is any suspicion that a child may be at risk of Congenital Toxoplasmosis, he/she should be tested for regularly for anti-Toxoplasma antibodies following birth; Toxoplasma IgG antibodies should decrease by approximately a half every month in uninfected individuals but will not disappear by 12 months in infected individuals.

Blog Overview

September 14th 2019
Immunoassays Infectious Diseases
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Logical Biological has added Chagas antibody positive plasma to its range having received clearance from the UK government Health & Safety Executive to handle human biological material containing Trypanosoma cruzi, which is the causative agent of Chagas Disease. T. cruzi is a Hazard Group 3 pathogen according to “The Approved List of Biological Reagents”. Hazard Group 3 is defined as follows: “Can cause severe human disease and may be a serious hazard to employees; it may spread to the community, but there is usually effective prophylaxis or treatment available.”

As part of this process, the UK government has reviewed Logical Biological’s key risk assessments and standard operating procedures. Logical Biological has previously received clearance to handle human biological material infected with other Hazard Group 3 organisms such as HIV, Hepatitis B, Hepatitis C, Malaria (Plasmodium falciparum) and Tapeworm (Taenia solium).

You can see the full list of infectious disease materials offered by Logical Biological here.

Logical Biological has received clearance from the UK government Health & Safety Executive to handle human biological material containing Trypanosoma cruzi, which is the causative agent of Chagas Disease. T. cruzi is a Hazard Group 3 pathogen according to “The Approved List of Biological Reagents”. Hazard Group 3 is defined as follows: “Can cause severe human disease and may be a serious hazard to employees; it may spread to the community, but there is usually effective prophylaxis or treatment available.”

As part of this process, the UK government has reviewed Logical Biological’s key risk assessments and standard operating procedures. Logical Biological has previously received clearance to handle human biological material infected with other Hazard Group 3 organisms such as HIV, Hepatitis B, Hepatitis C, Malaria (Plasmodium falciparum) and Tapeworm (Taenia solium).

You can see the full list of infectious disease patient material offered by Logical Biological here. Please contact us for further information on any of our plasma/serum, antigen and monoclonal antibody products for IVD.

Blog Overview

August 15th 2019
Company News Infectious Diseases Serum & Plasma
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Human Immunodeficiency Virus (HIV) has a reputation for being difficult to treat, although advances in medicine have reached a level where those being treated can be expected to live almost to their full life span. However, as we shall see in this article, current HIV testing is not perfect and many challenges remain.

There are multiple HIV viruses

HIV is actually a small family of distinct viruses comprised of HIV1 and HIV2. HIV1 accounts for 95% of worldwide HIV infections, while HIV2 is largely concentrated in West Africa. The two viruses are genetically related yet clearly distinct; HIV2 is less infectious than HIV1 and progresses more slowly. The two viruses also respond differently to some drug therapies; for example, HIV2 is less responsive than HIV1 to enfuvirtide and non-nucleoside reverse-transcriptase inhibitors. Nevertheless, it is essential that any medical diagnostic test can detect both viruses.

Further complicating matters, within HIV1 there are many different, i.e. genetically distinct, virus subtypes, some of which are extremely rare. How can HIV disease diagnosis test manufacturer ensure their test detect HIV1 subtype N when only a handful of such infections have ever been recorded? Clearly, the patient material needed to check that subtype N is detected cannot be readily available.

HIV Strains and Subtypes

Diagnosing newly-infected patients

One convenient and successful way of diagnosing HIV antibodies is to look for evidence of an immune response in the patient, i.e. does the patient’s blood contain antibodies raised against HIV? Human IgM and IgG anti-HIV antibodies can be readily detected using HIV antigens, typically in the form of synthesised peptides or recombinant proteins. But what if the patient has only just become infected and has not yet developed an immune response to the virus?

If such patients are only tested for antibodies to HIV they could receive a negative test result and then unknowingly go on to infect other individuals. It would be ideal to be able to effectively diagnose newly infected patients and this is why HIV p24 antigen tests are used. p24 is an abundant protein within HIV, making up most of the viral core. Unfortunately, although p24 is detectable earlier than the patient’s antibody response, p24 is not immediately present at detectable levels in the patient; there is still a “window” of time where a newly infected individual will test negative.

Post-infection timeline for HIV component detectability

Different patients, different responses

Each type of HIV test has a known post-infection time window during which it cannot be expected to detect HIV in patients. However, there is a strong intra-patient variation when each test becomes positive. As an example, Hurt et al. (2017)1 noted that 4th generation tests (inclusive of p24 testing) are positive for 50% of infected individuals at day 17.8, 75% at day 23.6 and 99% at day 44.3. This is why it is so important to test each patient for a battery of different viral and host components, as in 4th generation testing, as some components may be absent in a given patient.

Post-infection HIV and host components – typical levels & timeline

Access to Patient Material

The disease diagnosis community needs ready access to HIV patient material for use in assay development, assay calibration and quality control of HIV tests. Different strains, subtypes, ages, genders and stages of infection may be required. Companies such as Logical Biological specialise in this area, working directly with donor collection centres.

Niche scenarios

Babies carry their mother’s antibodies for the first months of their lives so tests to detect antibodies in the babies blood would be expected to be positive even if the baby is not infected. In this not so unusual scenario of a baby being born to a HIV-infected mother, as well as a few others, a test for Viral Load may be beneficial. Viral load tests for HIV use Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) to amplify HIV RNA if present in the blood. These tests are complex and expensive to perform, and no tests of this type have been approved for diagnostic use by the FDA.

Presence of HIV in donated blood

Donated blood products could be infectious, as some donators are not aware that they are infected. While individuals at high-risk of infection are discouraged from donating, clearly there is a risk of infection being spread through donated blood and this is mitigated by testing all such blood for a number of different infectious diseases. The National Health Service in the UK tests all donated blood for Syphilis, Hepatitis B (HBV), Hepatitis C (HCV), Hepatitis E (HEV), Human T Lymphotrophic Virus and (HTLV)5.

Some other infections are tested for in addition depending on the donator’s individual circumstances. Donated blood is typically tested using the RT-PCR method. Worryingly perhaps, this test is also not perfect; the risk of spreading infection through donated blood cannot be eliminated entirely. Patients won’t be positive for the HIV viral load test until a few days post-infection, and the time-window is even a few days longer where patient material is pooled, and thus diluted.

Self-testing & In-Field Testing

Not every unknowingly infected HIV patient would be willing to go to a clinic to get tested, even if they understand they are at high-risk and fear they might be infected. Partially addressing this problem, a market has developed around self-testing of HIV at home, and it is now straightforward to buy such tests from any self-respecting online retail giant.

Alternatively, imagine a remote rural location in a country with limited healthcare infrastructure – individuals might not be able to get to a clinic even if they wanted to. It is up to governments, regulators and assay developers to adapt to this need and by doing so they will improve the protection of the public and make a contribution to alleviating the HIV epidemic. It is noted that in one of the worse affected countries – South Africa – 90% of people living with HIV are now aware of their status, up from 66% in 20146; progress is being made.

Conclusions

The disease diagnosis community has made great strides in improving HIV detection. However, many challenges remain owing to the biology of the virus and its human hosts, human behaviour and the individual circumstances of those infected. Future trends are likely to see an increase in home/self-testing and movement towards 5th generation assays which give individual results for HIV1, HIV2 and p24 in the initial test providing valuable information to determine the most appropriate treatment for the particular individual.

References:

  1. Selecting an HIV Test: A Narrative Review for Clinicians and Researchers. Hurt CB, Nelson JAE, Hightow-Weidman LB, Miller WC. Sex Transm Dis. 2017 Dec;44(12):739-746.
  2. Human anti-HIV IgM detection by the OraQuick ADVANCE® Rapid HIV 1/2 Antibody Test. Guillon
    G    , Yearwood G, Snipes C, Boschi D, Reed MR. PeerJ. 2018 Feb 28;6
  3. Dynamics of HIV viremia and antibody seroconversion in plasma donors: implications for diagnosis and staging of primary HIV infection. Fiebig EW, Wright DJ, Rawal BD, Garrett PE, Schumacher RT, Peddada L, Heldebrant C, Smith R, Conrad A, Kleinman SH, Busch MP. AIDS. 2003 Sep 5;17(13):1871-9.
  4. Assessment of the Ability of a Fourth-Generation Immunoassay for Human Immunodeficiency Virus (HIV) Antibody and p24 Antigen to Detect both Acute and Recent HIV Infections in a High-Risk Setting. J Clin Microbiol. 2009 Aug; 47(8): 2639–2642. Mark W. Pandori, John Hackett, Jr., Brian Louie, Ana Vallari, Teri Dowling, Sally Liska, Jeffrey D. Klausner.
  5. https://www.blood.co.uk/the-donation-process/further-information/tests-we-carry-out/
  6. https://www.avert.org/professionals/hiv-around-world/sub-saharan-africa/south-africa
  7. https://www.avert.org/professionals/hiv-science/types-strains

 

Blog Overview

April 5th 2019
Infectious Diseases
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April 18th 2024
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