Report of two cases of influenza virus A/H1N1v and B co-infection during the 2010/2011 epidemics in the Italian Veneto Region
- Arianna Calistri†1, 2,
- Cristiano Salata†1, 2,
- Marina Cosentino1, 2,
- Samuele Asnicar2,
- Elisa Franchin1, 2,
- Riccardo Cusinato2,
- Monia Pacenti2,
- Isabella Donatelli3 and
- Giorgio Palù1, 2Email author
© Calistri et al; licensee BioMed Central Ltd. 2011
Received: 28 July 2011
Accepted: 3 November 2011
Published: 3 November 2011
From October 2010 to April 2011, in the Italian Veneto Region, 1403 hospitalized patients were tested for influenza virus infection by specific real time RT-PCR. Overall, 327 samples were positive for either influenza A (75%) or B (25%) viruses. Among these positive patients two resulted co-infected by A/H1N1v and B viruses. Even though co-infection with both influenza A and B viruses appears to be a rare event, it occurs naturally and may play a role in epidemiology and pathogenicity. In the present study the two co-infected patients were a transplant recipient immunocompromised adult and a child displaying a severe respiratory illness. The co-infection was confirmed by inoculation of the nasopharyngeal swabs in MDCK.2 cells, followed by immunofluorescence and real time RT-PCR assays. Moreover, in the case of the adult patient, the immune system response against both viruses was assayed by hemoagglutination inhibition test against reference influenza virus strains. Both patients fully recovered from infection, without significant differences with mono-infected patients.
Analysis performed for the identification of the two double positive samples.
real time RT-PCR
real time RT-PCR
Kinetic of viral clearance in nasal swabs of patient n° 1.
DAYS OF COLLECTION
A second case of co-infection by influenza A/H1N1v and B viruses was found in a 6 month old child, displaying severe respiratory symptoms and pneumonia. The 15th of February the child had undertaken antibiotic treatment by intravenous and nebulised routes. The 18th of February the real time RT-PCR assay showed the presence of both influenza virus type B and A, with levels of influenza B virus roughly 10 times higher (Ct 30, 76) with respect to the ones displayed by the A/H1N1v virus (Ct 32, 86). The child did not underwent antiviral treatment, the clinical symptoms and signs resolved quickly and the 22nd of February he was discharged without further virological analysis.
Dual infections of influenza A and B viruses appear to be a rare event and only few publications have reported simultaneous infection by two different types of influenza viruses in humans [3–7]. Thus, the factors that may be responsible for such events are not clear yet, even though the host immune system and the virus properties have been suggested [3–7]. It is interesting to note that both co-infected patients reported in this study represented individuals with a weak immune system, being a kidney transplant recipient and a 6 month year old child, thus suggesting that, indeed, the immunological state of the patient may play an important role in the co-infection establishment. Moreover, the child described in this study represents, to our knowledge, the first report of a dual infected patient with a clinical complication (pneumonia). Indeed, in all publications clinical manifestations in co-infected individuals were identical to those observed in single infections, with classical symptoms, without any clinical complication. However, it has to be mentioned that both these latter observations may be related to the specific cohort (hospitalized patients) taken into consideration in the current study. Thus a clear correlation between dual-infection and immunodeficiency/maturation, or dual infection and severity of the disease cannot be absolutely concluded by these data. On the other hand, both patients fully recovered. An oseltamivir based treatment was adopted only in the case of the adult patient, justified by his immunodeficiency state more than by the severity of the symptoms which remain mild till the viral clearance.
Finally, in contrast with previous literature data , in our two cases we did not observe significant differences in the RNA levels of the two viruses in the initial sample, a part for a slight higher amount of influenza B virus in the case of the child (roughly 10 times). However, in the case of the adult patients, for whom three sequential samples were analysed (Table 2), we observed a different kinetic in the viral clearance, with the influenza B virus becoming undetectable more rapidly than the influenza A virus. This finding may related to a different in vivo replication efficiency of two viruses. In fact, influenza A infections are usually more severe than those related to influenza B. However, further studies would be needed to support this hypothesis.
This work was supported by the 2009-CCM grant (Programma di sorveglianza virologica dell'influenza epidemica e pandemica per la stagione 2009/2010: rafforzamento della rete influnet) to GP e ID, grants from the Regione Veneto (2010) to GP and University of Padova (Ex-60%) to AC, CS, GP.
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