- Top of page
- Methods and materials
Influenza is a highly infectious, acute viral respiratory illness that causes worldwide outbreaks of variable extent and severity each year. Recently, the pandemic 2009 influenza A (H1N1) virus spread rapidly, resulting in millions of laboratory-confirmed cases and over 16 713 deaths in over 200 countries. Since then, numerous epidemiological and clinical findings on this influenza strain have been reported. However, few reports have evaluated viral shedding in patients admitted for 2009 H1N1 influenza and treated with oseltamivir.
The duration of viral shedding is likely to be an important determinant of infectivity and transmissibility and should be known when developing measures to prevent and control viral diseases. In the case of seasonal influenza viruses, the mean duration of viral shedding has been reported to be 4·8 days, although this virus has also been detected for up to 5–7 days in patients admitted to hospital. With regard to the 2009 H1N1 influenza strain, the World Health Organization (WHO) has recommended that patients receive 5 days of treatment with antiviral agents. However, animal models show that the 2009 H1N1 virus replicates more efficiently than seasonal influenza viruses in the respiratory tract.[5-7] In addition, several studies have shown that the 2009 H1N1 virus can still be present for 8 days or more.[8-12] Hence, some patients require additional antiviral treatments and need to be isolated to prevent infection. However, despite these observations, there are still no guidelines or recommendations stipulating that patients should be assessed by RT-PCR testing when antiviral treatment courses are completed to determine whether viral shedding is still occurring.
The aim of this study was to determine the incidence of prolonged viral shedding of 2009 H1N1 influenza in patients treated for 5 days with oseltamivir. Factors that promoted prolonged viral shedding were also identified.
- Top of page
- Methods and materials
During this study period, 20 913 nasopharyngeal swab samples were obtained and tested by RT-PCR. Of these, 8016 (38·3%) samples were found to be positive for 2009 H1N1 influenza. Patients with 2009 H1N1 were hospitalized if they developed potentially serious medical conditions or if the exacerbation of their underlying chronic illnesses or their severe symptoms was considered to be unmanageable at home. In total, 173 patients were admitted to isolation rooms and RT-PCR tests were repeated after 5 days of oseltamivir treatment according to our institutional protocols.
The baseline characteristics of our patient subjects, including their demographic variables, comorbidities, presenting symptoms, and initial laboratory parameters, were assessed. The mean age was 43·4 ± 20·6 years and 102 patients were male (58·9%). During the study period, 94 (54·3%) patients exhibited abnormal findings upon chest radiography that were consistent with pneumonia and nine patients (5·2%) died during this period. The median interval from symptom onset to hospital visitation was 2·0 (range, 1·0–4·0) days, while the median duration between symptom onset and oseltamivir initiation was 2·0 (range, 1·0–4·0) days. Of the 173 patients who underwent repeated RT-PCR on day 5, 88 cases had positive results (50·8%).
The data for the RT-PCR-positive and RT-PCR-negative groups were compared (Table 1). The presence of any major comorbidities or steroid treatments delayed oseltamivir therapy (two or more days after symptom onset). The continuation of respiratory symptoms 5 days after the start of treatment was significantly associated with prolonged viral shedding. Multivariate analysis revealed that prolonged viral shedding was significantly associated with delayed antiviral therapy (OR 2·74, 95% CI 1·29–5·82), major comorbidities (OR 3·07, 95% CI 1·29–7·32), and continuing respiratory symptoms after 5 days of treatment (OR 4·13, 95% CI 2·10–8·11) (Table 2).
Table 1. Clinical characteristics of 173 patients with laboratory-confirmed 2009 H1N1 influenza who were treated for 5 days with oseltamivir and then underwent a follow-up RT-PCR test
| ||RT-PCR-negative (n = 85)||RT-PCR-positive (n = 88)|| P |
|Age (y)||43·49 ± 18·81||45·13 ± 23·57||0·61|
|Male, n (%)||49 (57·6)||53 (60·2)||0·73|
|Vaccinationa, n (%)||17 (20·0)||23 (26·1)||0·67|
|Comorbidities, n (%)|
|Hypertension||14 (16·5)||20 (22·7)||0·30|
|Diabetes mellitus||11 (12·9)||13 (14·8)||0·73|
|Obstructive lung disease||11 (12·9)||17 (19·3)||0·26|
|Other underlying lung disease||22 (25·9)||28 (31·8)||0·39|
|Malignancy||17 (20·0)||26 (29·5)||0·15|
|Any major comorbidities||47 (55·3)||71 (80·7)||<0·01|
|Use of immunosuppressant||7 (8·2)||8 (9·1)||0·84|
|History of steroid use||14 (16·5)||25 (28·4)||0·06|
|Present symptoms, n (%)|
|Fever||72 (85·7)||72 (81·8)||0·49|
|Cough||75 (89·3)||80 (90·9)||0·72|
|Sore throat||34 (40·5)||23 (26·1)||0·05|
|Rhinorrhea||28 (33·3)||33 (37·5)||0·57|
|Gastrointestinal symptoms||16 (19·0)||12 (13·6)||0·34|
|Treatment modality, n (%)|
|Antibiotics treatment||61 (71·8)||72 (81·8)||0·12|
|Steroid treatment||23 (27·1)||41 (46·6)||<0·01|
|High-dose oseltamivir (150 mg)||43 (50·6)||42 (47·7)||0·71|
|Other antiviral agent combinationb||6 (7·1)||14 (15·9)||0·07|
|Oseltamivir therapy commenced two or more days after symptom onset||42 (49·8)||58 (65·9)||<0·01|
|White blood cell count (109/l)||9·06 ± 4·47||8·88 ± 5·88||0·83|
|Absolute neutrophil count||7327·0 ± 4393·8||7079·4 ± 5451·1||0·76|
|Lymphocyte (%)||14·4 ± 10·0||15·9 ± 13·6||0·51|
|Lymphocyte count (109/l)||1030·9 ± 554·5||999·3 ± 800·0||0·78|
|Hemoglobin (g/dl)||12·9 ± 3·7||12·1 ± 3·0||0·18|
|Platelet count (109/l)||179·9 ± 87·4||176·5 ± 92·8||0·82|
|Aspartate transaminase (IU/l)||324·4 ± 212·1||67·5 ± 76·3||0·50|
|Alanine transaminase (IU/l)||175·3 ± 103·2||37·2 ± 36·6||0·40|
|C-reactive protein (mg/dl), (N = 146)||8·2 ± 8·5||8·27 ± 9·4||0·97|
|Procalcitonin (ng/ml), (N = 78)||3·4 ± 7·7||5·6 ± 13·2||0·39|
Table 2. Multivariate analysis of factors associated with prolonged viral shedding in patients with laboratory-confirmed 2009 H1N1 influenza who were treated for 5 days with oseltamivir
| ||Multivariate analysis|
|Odds ratio||95% CI|| P |
|Oseltamivir therapy commenced two or more days after symptom onset||2·74||1·29–5·82||<0·01|
|Any major comorbidities||3·07||1·29–7·32||<0·01|
|Respiratory symptoms continuing on the 5th day of treatment||4·13||2·10–8·11||<0·01|
- Top of page
- Methods and materials
The duration of viral shedding provides important information regarding infectivity and transmissibility. However, only a few studies to date have described the duration of 2009 H1N1 shedding. Na et al. reported that the median duration of viral shedding of 2009 H1N1 influenza, assessed by RT-PCR, was 9 days. Moreover, a further report from France has indicated a median shedding duration of 11 days for this virus. Hence, these studies show that the shedding period of 2009 H1N1 influenza is longer than that of seasonal influenza strains. Therefore, although the WHO recommends that influenza should be treated by 5 days of antiviral therapy, viral shedding may persist beyond this period and additional treatment and isolation should be considered for some infections. In our present study, the shedding of 2009 H1N1 virus was assessed in 173 patients: after 5 days of oseltamivir treatment, 88 patients (50·8%) still had a positive RT-PCR result. These results agree with those of recent studies that found that patients admitted to hospital with the pandemic influenza 2009 H1N1 virus had a longer duration of viral shedding than adults who were hospitalized with a seasonal influenza virus infection.[12-14]
In seasonal influenza, prolonged viral shedding can occur in children, immunocompromised people, and elderly hospitalized patients with comorbidities. With regard to 2009 H1N1 influenza, Ling et al. have reported that younger immunocompetent adults show prolonged shedding, while Cao et al. have suggested that a delay from the onset of symptoms to oseltamivir therapy of >48 hours is associated with persistent RT-PCR positivity (>5 days). In our present study, the presence of major comorbidities was also found to be significantly associated with a persistent and positive RT-PCR result 5 days after oseltamivir therapy. The major comorbidities consisted of chronic systemic medical illnesses, which included cancer, chronic lung disease, renal diseases, heart disease, liver diseases, and stroke.
Our present findings show that prolonged shedding is also associated with the presence of respiratory symptoms after 5 days of antiviral therapy and the commencement of antiviral therapy two or more days after symptom onset. These results agree with those of previous studies.[13, 18] A recent Italian study has reported that the duration of viral shedding is significantly reduced when therapy is initiated within 2 days of symptom onset.
The Current Centers for Disease Control and Prevention Guidelines recommend that persons with influenza should not return to work or school until 24 hours after their fever has resolved without the use of antipyretics. These guidelines are based on studies showing that shedding can occur after fever resolution and that many people infected with influenza will not have a fever. Our present study also shows that prolonged shedding is associated with the continuing presence of respiratory symptoms (defined as cough, sore throat, rhinorrhea, and nasal obstruction) after 5 days of antiviral therapy. This is consistent with the results of a previous study in which the 2009 H1N1 influenza virus was found to be frequently detectable by RT-PCR for up to 10 days after fever resolution. Hence, it should be considered that if respiratory symptoms remain after 5 days of antiviral treatment, additional antiviral treatment and isolation may be needed, especially if the patient commenced antiviral therapy more than 2 days after the onset of symptoms. However, further research is needed to clarify the effects of additional antiviral treatment and isolation.
Antiviral therapy has been proven to reduce the viral shedding period of seasonal influenza.[22-24] Oseltamivir (a neuraminidase inhibitor) is a first-line influenza drug that has been shown to effectively reduce both the severity of symptoms and the duration of infection. In our present study, 75 and 150 mg of oseltamivir were administered twice daily for simple and complicated influenza infections, respectively. These two doses of oseltamivir do not differ significantly in terms of reducing viral shedding and titers in naturally acquired influenza infections.[22-24] In the present study, we found there is no significant difference in viral shedding between high dose of oseltamivir and standard dose (P = 0·71).
The severity of the (H1N1) 2009 influenza pandemic correlates with the extent of lymphopenia. In particular, Li et al. showed that the viral load correlates inversely with the absolute lymphocyte counts in untreated patients.[26, 27] However, in our present study, a significant correlation between the viral shedding period and lymphocyte count was not observed. In addition, viral shedding did not correlate with other laboratory data, including procalcitonin levels, leukocytosis, absolute neutrophil count, C-reactive protein levels, or liver enzyme levels.
This study has several noteworthy limitations. First, as this study included patients who were treated with oseltamivir, the data do not reflect the natural viral shedding period but the shedding period in patients treated with oseltamivir for 5 days. Second, samples that are positive for viral RNA by RT-PCR may not contain live virus. Third, the samples were not analyzed at a quantitative level. Nevertheless, our preliminary data reveal associations between prolonged viral shedding in patients with 2009 H1N1 influenza who were treated with oseltamivir for 5 days and also various clinical characteristics of these cases. These observations may be pertinent for future epidemiological control in emergency department and in the clinical management of influenza.