Early occurrence of influenza A epidemics coincided with changes in occurrence of other respiratory virus infections

Abstract

Background: Viral interaction in which outbreaks of influenza and other common respiratory viruses might affect each other has been postulated by several short studies. Regarding longer time periods, influenza epidemics occasionally occur very early in the season, as during the 2009 pandemic. Whether early occurrence of influenza epidemics impacts outbreaks of other common seasonal viruses is not clear.

Objectives: We investigated whether early occurrence of influenza outbreaks coincides with shifts in the occurrence of other common viruses, including both respiratory and non-respiratory viruses.

Methods: We investigated time trends of and the correlation between positive laboratory diagnoses of eight common viruses in the Netherlands over a 10-year time period (2003-2012): influenza viruses types A and B, respiratory syncytial virus (RSV), rhinovirus, coronavirus, norovirus, enterovirus, and rotavirus. We compared trends in viruses between early and late influenza seasons.

Results: Between 2003 and 2012, influenza B, RSV, and coronavirus showed shifts in their occurrence when influenza A epidemics occurred earlier than usual (before week 1). Although shifts were not always consistently of the same type, when influenza type A hit early, RSV outbreaks tended to be delayed, coronavirus outbreaks tended to be intensified, and influenza virus type B tended not to occur at all. Occurrence of rhinovirus, norovirus, rotavirus, and enterovirus did not change.

Conclusion: When influenza A epidemics occured early, timing of the epidemics of several respiratory winter viruses usually occurring close in time to influenza A was affected, while trends in rhinoviruses (occurring in autumn) and trends in enteral viruses were not.

Keywords: Influenza; respiratory syncytial virus; seasonality; time trends; viral interference; virus interaction.

Figure 1

Time series of laboratory diagnoses* of common viruses 2003–2012 (early influenza A seasons depicted by gray‐shaded areas). *Absolute numbers of positive laboratory tests. The numbers of influenza A diagnoses were high during the 2009/2010 season due to the intensified testing that occurred during the A(H1N1)pdm09 pandemic and for graphical representation were reduced by a factor 13·1 in that season.

Figure 2

Three‐week moving averages of laboratory submissions for eight viruses stacked by season (2003/2004–2011/2012). Percentages are calculated over the total number of submissions per respective pathogen over the total study period. Influenza A counts during the 2009/2010 pandemic were scaled down to allow their fit into the graphs (see Methods). 2003/2004 data not available for coronavirus, norovirus, rotavirus, and enterovirus.

Figure A1

Three‐week moving average of influenza A diagnoses by season (2003/2004—2011/2012).

Figure A2

(A) Time series of influenza A and B and RS virus (early influenza A seasons depicted by gray‐shaded areas). (B) Time series of influenza A, rhinovirus, and coronavirus (early influenza A seasons depicted by gray‐shaded areas). (C) Time series of influenza A, norovirus, and rotavirus (early influenza A seasons depicted by gray‐shaded areas). (D) Time series of influenza A and enterovirus (early influenza A seasons depicted by gray‐shaded areas). (E) Time series of influenza A, mean temperature, and mean relative humidity (early influenza A seasons depicted by gray‐shaded areas).