EID Journal: H7N9 Antibodies In Close Contacts Of Known Cases

# 9637

 

Two big questions we always ask when we see human infections with novel viruses are 1) How easily is it transmitted to others?  and  2) What is the spectrum of illness produced by infection? 

 

While seemingly simple and straightforward questions, answering them isn’t easy. 

 

Most human infections with MERS-CoV, or Avian Flu (H5N1, H7N9, H10N8, etc.) look very much like any other respiratory infection – except that they often carry a higher mortality rate than seasonal influenza.  Unless you are specifically testing for these novel viruses, there really isn’t any way to accurately diagnose them. 

 

And testing, assuming it is available at all, is usually reserved for those sick enough to be hospitalized.

 

So we tend to get a skewed view of the severity of these novel viruses, as moderate, mild, or even sub-clinical infections are rarely documented. And if these less-than-severe cases aren’t being tested, we are also apt to under appreciate possible chains of transmission.

 

The `practical solution’ (as opposed to trying to test every ILI patient for an increasing array of novel viruses) is to monitor, and test, close contacts of the limited number of known (and usually severe) novel flu cases.  That way we can get an idea of the transmissibility of the virus, and can catalog its severity in secondary cases.

 

PCR testing is normally done during the contact’s incubation period to check for infection and/or viral shedding, and while usually applied to those showing physical symptoms, can sometimes pick up asymptomatic infections as well.

 

Several weeks post-exposure, it is also desirable to test a contact’s blood for virus-specific antibodies, which would indicate the patient had been exposed to, and fought off the virus.  Serological testing can often turn up mild, or sub-clinical infections that would otherwise not have been detected.

 

There are, of course, limitations to serological testing, just as there are to PCR tests and viral cultures.  No lab test is perfect.  

 

Disagreements exist over what constitutes a `positive’  serological test (usually defined as a 4-fold increase in post-exposure antibody titer levels), and there are always concerns over potential cross-reactive antibodies and false positives.

 

But serological studies are generally regarded as the best way to determine the incidence of a viral infection in a population, as you don’t have to depend upon a `perfect catch’ of a biological sample while the patient is actively shedding virus particles. 

 

All of which brings us to an EID Journal Letter, published ahead of print, that details serological testing of 225 close contacts of 7 H7N9-infected patients during China’s first two epidemic waves. The authors found 22 contacts (9.8%) with elevated HI H7N9 antibody titers (>1:40).

 

While none of these contacts were overtly symptomatic during the incubation period, the authors believe this finding suggests that H-2-H transmission of the H7N9 virus may occur among close contacts of infected cases.

 

Some excerpts follow, click the link to read the entire letter.

 

Volume 21, Number 4—April 2015

Letter

Avian Influenza A(H7N9) Virus Antibodies in Close Contacts of Infected Persons, China, 2013–2014

To the Editor: From early 2013 (1) through November 2014, >460 human cases of laboratory-confirmed avian influenza A(H7N9) virus infection occurred in China. Although human-to-human transmission of subtype H7N9 virus is not common, evidence has been reported of probable transmission among several family clusters (2), between 2 household contacts (3), and between a doctor and an infected patient (4). Taken together, these observations suggest that family members, health care providers, and other close contacts (hereafter called contacts) of H7N9-infected persons may be at risk for infection.

In China, national guidelines regarding H7N9-infected patients call for observation of contacts for 7 days after exposure for signs and symptoms of infection and, if any occur, collection of throat swab specimens for testing by molecular assays (5). The guidelines do not call for serologic testing. Because human avian influenza infections may be mild or asymptomatic, we sought to determine whether serologic testing would show evidence of H7N9 virus infection among contacts of infected persons during the 2013–2014 epidemic in China. Contacts were defined in accordance with China’s guidelines for prevention and control of human H7N9 virus infection (5,6). The institutional review board of Wuxi Center for Disease Control and Prevention, Wuxi, Jiangsu Province, China, reviewed and approved this study.

<SNIP>

Serologic assay results showed that, 14–28 days after their earliest exposure to an H7N9-infected patient, 22 (9.8%) contacts had elevated HI antibody titers (>1:40) against H7N9 virus; titers were 1:40 for 17 contacts and 1:80 for 5 contacts. Positive results for all 22 serum samples were validated by microneutralization assay; 15 (68.2%) samples had microneutralization antibody titers of >1:10 against H7N9 virus antigen (Table). Of the contacts with an HI titer of >1:80 and microneutralization titer of >1:40, 3 were nurses, 1 was a nurse assistant, and 1 was a family member (a patient’s daughter). All 5 of these contacts had antibody titers of <1:40 to influenza subtype H1N1, H5N1, and H9N2 viruses, and 2 of the nurses had HI antibody titers of 1:80 against subtype H3N2 virus. All contacts denied having influenza-like respiratory symptoms during the 28 days of follow-up and also denied recent exposure to poultry or pigs or their environments. Of contacts with an HI titer of >1:80 to seasonal H1N1 virus, 3 had titer of 1:80, and 1 each had titer of 1:160 or 1:640. Of the 225 contacts, 108 had HI titers >1:80 against seasonal H3N2 virus (1:80 for 63 contacts, 1:160 for 27 contacts, 1:320 for 9 contacts, and >1:640 for 8 contacts). All contacts had influenza subtype H5N1 and H9N2 antibody titers of <1:80.

<SNIP>

A limitation of our study is that we did not collect serum samples from all contacts of infected persons or from controls; therefore, we could not assess the possibility of false-positive results or asymptomatic infections. However, our findings of elevated levels of subtype H7N9 antibody among 6.7% of contacts during this epidemic in China offer evidence that human-to-human transmission of H7N9 virus may occur among contacts of infected persons.

Mai-Juan Ma¹, Guang-Yuan Ma¹, Xiao-Xian Yang¹, Shan-Hui Chen¹, Gregory C. Gray, Teng Zhao, Jing Bao, Jing-Jing Zhou, Yan-Hua Qian, Bin Lu, Xia Ling², and Wu-Chun Cao²

BMC: Decline Of Antibody Titers With A(H1N1)pdm Over Time

Credit NIAID

 

 

# 8875

 

The arrival of a novel H1N1 influenza pandemic virus in 2009 – the first one in more than 40 years – has provided researchers with unique opportunities to observe how a newly introduced flu virus behaves in humans, and quite frankly, in other species as well (see The 2009 H1N1 Virus Expands Its Host Range (Again)).

 

Serological studies that would have been impractical before on H3N2 or the old seasonal H1N1 virus – due to decades of ongoing exposure to these strains – suddenly became possible with a new flu in town.

 

One of the unanswered questions surrounding our immune response to influenza infection is how long does our acquired immunity last?  

 

Admittedly, the answer to that question will vary from one person to the next, and depend on a variety of factors including the strain of flu, the person’s age, general health, and state of their immune system.  And there seems to be a difference between the duration of immunity gained from actual infection vs. through vaccination.

 

Despite circulating now for more than 5 years, the (now seasonal) H1N1 virus remains antigenically very similar to the pandemic strain that emerged in the spring of 2009.  So much so that an an A/California/7/2009 (H1N1)pdm09-like virus will be used for the sixth year running in the flu vaccine. 

Yet, despite having a half of decade of vaccination and natural exposure to this new H1N1 virus, last year saw a particularly heavy H1N1 flu season in North America. Normally, we’d look to antigenic drift to explain a major resurgence of a seasonal flu virus after several years, but H1N1 has been remarkably (albeit, not totally) stable in that regard.

   

Drift is the standard evolutionary path of influenza viruses, and comes about due to replication errors that are common with single-strand RNA viruses (see NIAID Video: Antigenic Drift) Drift is primarily responsible for the need to change flu vaccine strains every couple of years (something that is yet to happen with H1N1).

 

Another possibility is waning immunity, something that is recognized (particularly with vaccines, and among the elderly), but has been difficult to quantify in the past.  Given the immune system’s tabula rasa with regards to the 2009 H1N1 virus, it has become possible to track the decline of antibody titers of a cohort of individuals who were first exposed five years ago.

 

Rate of decline of antibody titers to pandemic influenza A (H1N1-2009) by hemagglutination inhibition and virus microneutralization assays in a cohort of seroconverting adults in Singapore

Jung Pu Hsu, Xiahong Zhao, Mark I-Cheng, Alex R Cook, Vernon Lee, Wei Yen Lim, Linda Tan, Ian G Barr, Lili Jiang, Chyi Lin Tan, Meng Chee Phoon, Lin Cui, Raymond Lin, Yee Sin Leo and Vincent T Chow

BMC Infectious Diseases 2014, 14:414  doi:10.1186/1471-2334-14-414

Published: 28 July 2014

Abstract (provisional)

Background

The rate of decline of antibody titers to influenza following infection can affect results of serological surveys, and may explain re-infection and recurrent epidemics by the same strain.

Methods

We followed up a cohort who seroconverted on hemagglutination inhibition (HI) antibody titers (>=4-fold increase) to pandemic influenza A(H1N1)pdm09 during a seroincidence study in 2009. Along with the pre-epidemic sample, and the sample from 2009 with the highest HI titer between August and October 2009 (A), two additional blood samples obtained in April 2010 and September 2010 (B and C) were assayed for antibodies to A(H1N1)pdm09 by both HI and virus microneutralization (MN) assays. We analyzed pair-wise mean-fold change in titers and the proportion with HI titers >= 40 and MN >= 160 (which correlated with a HI titer of 40 in our assays) at the 3 time-points following seroconversion.

Results

A total of 67 participants contributed 3 samples each. From the highest HI titer in 2009 to the last sample in 2010, 2 participants showed increase in titers (by HI and MN), while 63 (94%) and 49 (73%) had reduction in HI and MN titers, respectively.

Titers by both assays decreased significantly; while 70.8% and 72.3% of subjects had titers of >= 40 and >= 160 by HI and MN in 2009, these percentages decreased to 13.9% and 36.9% by September 2010. In 6 participants aged 55 years and older, the decrease was significantly greater than in those aged below 55, so that none of the elderly had HI titers >= 40 nor MN titers >= 160 by the final sample.

Due to this decline in titers, only 23 (35%) of the 65 participants who seroconverted on HI in sample A were found to seroconvert between the pre-epidemic sample and sample C, compared to 53 (90%) of the 59 who seroconverted on MN on Sample A.

Conclusions

We observed marked reduction in titers 1 year after seroconversion by HI, and to a lesser extent by MN. Our findings have implications for re-infections, recurrent epidemics, vaccination strategies, and for cohort studies measuring infection rates by seroconversion.

The complete article is available as a provisional PDF. The fully formatted PDF and HTML versions are in production.

 

The entire study is available, and well worth reading, but I’ve excerpted two paragraphs below that sum up their findings.  

Discussion

The objective of our study was to understand temporal changes in antibody titers following seroconversion during the initial epidemic of A(H1N1)pdm09 infections in  Singapore. Our results revealed a fairly rapid decline in antibody titers following seroconversion, with only a fifth of those who originally had HI titers of  ≥40 and half of those with MN titers of  ≥160 still  having  titers  above  the  respective  cut-off  points  after  a  year.  There  was  also  some indication  that  the  rate  of  decline  was  higher  in  older  individuals,  and  that  the  change  in antibody  titers  measured  by  HI  was  greater  than  by  MN.  Symptomatic  infections  were associated with higher starting antibody titers, and continued to have marginally higher titers in subsequent samples, at least by MN assays.

<SNIP>

Conclusions

Six  months  and  one  year  after  antibodies  peaked  following  presumptive  infection  with A(H1N1)pdm09, only 25% and 14% of participants respectively had antibody  titers against A(H1N1)pdm09 that would be considered protective (HI titer ≥40). The decline in antibody titers may explain susceptibility to re-infections, and recurrent epidemics following the initial epidemic of infections during the pandemic. It also suggests that influenza vaccination may have to be administered more frequently in the tropics where there is year-round circulation of influenza viruses. The rate of decline in elderly individuals may be even more rapid, and if our  findings  are  confirmed,  may  necessitate  alternative  strategies  of  influenza  vaccine development for this vulnerable group.

 

 

A pretty good reminder that even if you got the vaccine last year – or worse, endured the flu last winter – you may not be carrying sufficient immunity forward into the new flu season to protect you against re-infection. 

 

And given that H3N2, and two lineages of Influenza B, are also in circulation – your risks of catching some kind of flu are compounded further.

 

Which is why, even though the H1N1 component of the flu vaccine remains unchanged this year, it is a good idea to get the flu vaccine every year.  

 

Despite variable and sometimes disappointing VE (Vaccine Effectiveness) numbers (see CIDRAP: A Comprehensive Flu Vaccine Effectiveness Meta-Analysis) - particularly among the elderly (see BMC Infectious Diseases: Waning Flu Vaccine Protection In the Elderly) - we continue to see evidence of substantial benefit from the flu shot.

 

For more, you may wish to revisit:

 

CDC: Flu Shots Reduce Hospitalizations In The Elderly

Research: Low Vaccination Rates Among 2013-2014 ICU Flu Admissions

Two Studies On The 2009 Pandemic Flu Vaccine & Pregnancy

CDC: New Tests Reveal Illinois `MERS’ Case Was Never Infected

Credit CDC PHIL

 

# 8676

 

With lab tests, we’d all like to believe that results are always binary; either positive or negative - with no ambiguity - and certainly no false readings. The two main measures of the accuracy of any diagnostic test are sensitivity and specificity.

• Sensitivity is defined as the ability of a test to correctly identify individuals who have a given disease or condition.

• Specificity is defined as the ability of a test to exclude someone from having a disease or illness.

 

But the truth is, all lab tests have limitations.  And the MERS serological tests currently being used and evaluated by the CDC are no exception.

Just over 10 days ago the big infectious disease story was: CDC: Contact Of Indiana MERS Case Tests Positive For The Virus. 

 

The contact was reportedly well, but based on early testing - had seroconverted – developed antibodies to the virus indicating prior infection. Today, at a 1pm press conference announced late this morning, the CDC has backtracked on those findings, after more complete testing has been completed.

 

Press Release

Embargoed until 1 p.m. ET

Wednesday, May 28, 2014                                                                                                            

Contact: CDC Media Relations

(404) 639-3286

CDC concludes Indiana MERS patient did not spread virus to Illinois business associate

After completing additional and more definitive laboratory tests, CDC officials have concluded that an Indiana MERS patient did not spread the virus to an Illinois associate during a business meeting they had before the patient became ill and was hospitalized.

CDC and state and local public health officials are conducting voluntary testing of people who had contact with two travelers who went from Saudi Arabia to the U.S. where they were confirmed to have Middle East Respiratory Syndrome, or MERS.  One type of tests conducted by state and CDC labs uses respiratory samples and can quickly indicate if a person has active infection with the virus. These tests are called PCR, or polymerase chain reaction, assays.  Another type of testing, conducted on blood samples in CDC labs, is called serology and is designed to look for antibodies to Middle East Respiratory Syndrome Coronavirus (MERS-CoV). Antibodies would indicate that a person had been previously infected with the virus and developed an immune response. To conduct serology for MERS-CoV, CDC performs three separate tests – ELISA or enzyme-linked immunosorbent assay, IFA or immunofluorescent assay, and a third more definitive test called the neutralizing antibody assay which takes longer than the other two tests. 

The Illinois resident, a business associate who had extended face-to-face contact with the Indiana MERS patient, tested negative for active MERS-CoV infection by PCR in the days after his interaction with the man. Given the Illinois man’s contact with the MERS patient, CDC conducted serology testing to see if the Illinois man had antibodies to MERS-CoV.  Preliminary ELISA and IFA results announced by CDC on May 17 indicated that the Illinois resident appeared to be positive for MERS-CoV antibodies.  

“The initial ELISA and IFA serology results indicated the possibility that the Illinois resident had been previously infected with MERS-CoV,” said David Swerdlow, M.D., who is leading CDC’s MERS-CoV response.  “This compelled us to notify and test those people with whom he had close contact in the days following his interaction with the Indiana MERS patient.” 

CDC scientists have since tested additional blood samples and completed the slower, definitive serology test, the neutralizing antibody test, which requires at least five days before a result is available.  Based on the result of all of these tests, which require careful interpretation, CDC has concluded that the Illinois resident was not previously infected with MERS-CoV.  

“While we never want to cause undue concern among those who have had contact with a MERS patient, it is our job to move quickly when there is a potential public health threat,” said Swerdlow. “Because there is still much we don’t know about this virus, we will continue to err on the side of caution when responding to and investigating cases of MERS in this country.”

To date, active MERS-CoV infection has not been found in any of the contacts of the two people in the U.S. confirmed to have the disease.  However, investigations are ongoing, including voluntary serology testing of contacts.  This vigilant approach is intended to help CDC reduce any immediate public health threat, as well as help the global scientific community gain a better understanding of how MERS-CoV spreads so we can more effectively control this disease in the future.  There is currently no evidence of sustained spread of MERS-CoV in community settings.

As CDC continues to gather additional information, officials will update the agency’s MERS recommendations as needed.  At this time, CDC’s recommendations to the public, travelers, doctors and other healthcare providers have not changed.

Serological Testing Of 2012 Jordanian MERS Outbreak

Photo Credit NIAID

 

 

# 8625

 

Our first indication that a novel coronavirus was circulating in Saudi Arabia came from a September 2012 letter posted in ProMed Mail (NOVEL CORONAVIRUS - SAUDI ARABIA: HUMAN ISOLATE) by Dr. Ali Mohamed Zaki - an Egyptian Virologist working In Saudi Arabia. Retrospective analysis, however, showed the MERS coronavirus to have been involved in a pneumonia outbreak at a hospital in Jordan in April of that year.

That outbreak, which made headlines in the Middle East and was monitored by FluTrackers at the time, appeared to involve at least 11 people, 2 of whom died. 

 

Testing for `the usual pathogenic suspects’  found no identifiable cause for the illness. This happens more often than most people might imagine,  but since the outbreak appeared to be contained, it was temporarily forgotten.

 

After a handful of novel coronavirus cases were identified during the fall of 2012, retrospective testing was done on some of the samples taken from that outbreak, and in December 2012 (see Background and summary of novel coronavirus infection) we learned that at least 2 of those cases tested positive for nCoV (the old name for MERS-CoV).

Making this Jordanian hospital outbreak the earliest identified human infections from this emerging coronavirus.

Serological testing at the time was still in its infancy (in late 2012, only 9 cases had been identified), and so while more cases from this hospital were suspected, verifying that fact wasn’t possible at the time.

 

Fast forward to June of 2013 and Helen Branswell brought us her report on the research by Dr. Mohammad Al-Abdallat &  Dr. Mark Pallansch et al., that found evidence that at least 10 people had been infected during that earliest outbreak (see MERS-CoV: Early Serological Results).

. 

Helen interviewed Dr. Pallansch, Director of the CDC’s division of viral diseases, on the limitations of testing at the time:

 

He explained that there are still questions about the accuracy of blood tests for MERS, because labs like the CDC which have developed tests have been unable to validate them to this point. To do that, a lab needs both samples known to be negative and samples known to be positive to be sure the test finds only true cases. The only country with lots of positive blood samples is Saudi Arabia, and it is still working out an agreement with the CDC to share blood samples.

So the U.S. agency is using three different tests on the samples. They believe the tests are specific, meaning that positive results are likely true positives, Pallansch said. But they haven't been able to assess the sensitivity of the tests, meaning they cannot be sure that a negative result is a true negative.

 

All of which serves as prelude to a new study by these same researchers, which appeared yesterday in the journal Clinical Infectious Diseases, that seeks to further update, describe, and quantify this outbreak.

 

Hospital-associated outbreak of Middle East Respiratory Syndrome Coronavirus: A serologic, epidemiologic, and clinical description

Mohammad Mousa Al-Abdallat*,1, Daniel C. Payne*,2, Sultan Alqasrawi1,  Brian Rha2,3, Rania A. Tohme4, Glen R. Abedi2, Mohannad Al Nsour5,  Ibrahim Iblan6,  Najwa Jarour1, Noha H. Farag7,  Aktham Haddadin8,  Tarek Al-Sanouri8,  Azaibi Tamin2,  Jennifer L. Harcourt2,  David T. Kuhar9,  David L. Swerdlow2,  Dean D. Erdman2, Mark A. Pallansch2, Lia M. Haynes2,  Susan I. Gerber2, the Jordan MERS-CoV Investigation Team

Abstract

Background. In April 2012, the Jordan Ministry of Health (JMoH) investigated an outbreak of lower respiratory illnesses at a hospital in Jordan; two fatal cases were retrospectively confirmed by rRT-PCR to be the first detected cases of Middle East Respiratory Syndrome (MERS-CoV).

Methods. Epidemiologic and clinical characteristics of selected potential cases were assessed through serum blood specimens, medical chart reviews and interviews with surviving outbreak members, household contacts, and healthcare personnel. Cases of MERS-CoV infection were identified using three U.S. Centers for Disease Control and Prevention (CDC) serologic tests for detection of anti-MERS-CoV antibodies.

Results. Specimens and interviews were obtained from 124 subjects. Seven previously unconfirmed individuals tested positive for anti-MERS-CoV antibodies by at least two of three serologic tests, in addition to two fatal cases identified by rRT-PCR. The case fatality rate among the nine total cases was 22%. Six cases were healthcare workers at the outbreak hospital, yielding an attack rate of 10% among potentially exposed outbreak hospital personnel. There was no evidence of MERS-CoV transmission at two transfer hospitals having acceptable infection control practices.

Conclusion. Novel serological tests allowed for the detection of otherwise unrecognized cases of MERS-CoV infection among contacts of a Jordan hospital-associated respiratory illness outbreak in April 2012, resulting in a total of nine test-positive cases. Serologic results suggest that further spread of this outbreak to transfer hospitals did not occur. Most cases had no major, underlying medical conditions; none were on hemodialysis. Our observed case fatality was lower than has been reported from outbreaks elsewhere.

 

Since people who are infected with a virus only shed that virus at detectable levels for a limited amount of time (usually days, sometimes weeks) there is a narrow window of opportunity to test them using standard rRT-PCR techniques.

 

Creating, and validating serological tests - which can detect antibodies showing that a person has previously been infected - is our best hope for determining just how widespread a viral illness really is in any population.

 

Today’s study reconfirms a good deal of what was previously known, or suspected, about the Jordanian hospital outbreak. If confirms that at least 9 people were infected in this cluster.  It also indicates that the virus did not spread efficiently beyond the environs of the hospital, and suggests an attack rate of 10% among hospital employees. 

While it may seem more important to be able to detect where a virus currently is (detecting active infections via  rRT-PCR testing or viral culture), you really can’t begin to understand a virus’s behavior, or where it might be going, until you can figure out where it’s been.