Bacterial sinusitis and otitis media following influenza virus infection in ferrets

Abstract

Streptococcus pneumoniae is the leading cause of otitis media, sinusitis, and pneumonia. Many of these infections result from antecedent influenza virus infections. In this study we sought to determine whether the frequency and character of secondary pneumococcal infections differed depending on the strain of influenza virus that preceded bacterial challenge. In young ferrets infected with influenza virus and then challenged with pneumococcus, influenza viruses of any subtype increased bacterial colonization of the nasopharynx. Nine out of 10 ferrets infected with H3N2 subtype influenza A viruses developed either sinusitis or otitis media, while only 1 out of 11 ferrets infected with either an H1N1 influenza A virus or an influenza B virus did so. These data may partially explain why bacterial complication rates are higher during seasons when H3N2 viruses predominate. This animal model will be useful for further study of the mechanisms that underlie viral-bacterial synergism.

FIG. 1.

Nasal wash bacterial titers. Groups of 5 to 10 ferrets mock infected with PBS or infected with influenza virus A/Fujian/411/02 (H3N2), A/Sydney/5/97 (H3N2), A/Taiwan/1/86 (H1N1), or B/Singapore/222/79 were challenged with pneumococcus strain A.166 5 days later, and daily nasal washes were taken. The 25th to 75th percentiles of measurements collected on four consecutive days are represented by the shaded box plots, with the horizontal bar indicating the median value. Error bars indicate the standard deviation of the measurements. An asterisk indicates a significant difference (P < 0.05) compared to mock-infected animals.

FIG. 2.

Nasal wash viral titers. Groups of 5 to 10 ferrets mock infected with PBS or infected with influenza virus A/Fujian/411/02 (H3N2), A/Sydney/5/97 (H3N2), A/Taiwan/1/86 (H1N1), or B/Singapore/222/79 were challenged with pneumococcus strain A.166 5 days later, and daily nasal washes were taken. The 25th to 75th percentiles of measurements taken the first day after bacterial challenge are represented by the shaded box plots, with the horizontal bar indicating the median value. Error bars indicate the standard deviation of the measurements. TCID₅₀, 50% tissue culture infective dose.

FIG. 3.

Secondary bacterial infections in ferrets. Ferrets were infected with influenza virus, followed 5 days later by a bioluminescent variant of pneumococcus strain A.166. Daily imaging of live, anesthetized ferrets allowed visualization of secondary bacterial infections. Representative examples from single animals of A) nasopharyngeal colonization, B) sinusitis, and C) otitis media are pictured. The color bar on the right indicates the number of relative light units per pixel measured over 2 min. A posterio-anterior view and two lateral views of a ferret with concomitant sinusitis and otitis media are shown in D).

FIG. 4.

Histopathology of upper respiratory tract complications. Representative views of the nasal cavity (A and B) (magnification, ×10), frontal sinus (C and D) (magnification, ×20), eustachian tube (E and F) (magnification, ×40), and middle ear (G and H) (magnification, ×10) are shown for a ferret infected with A/Taiwan/1/86 (H1N1) which did not develop secondary bacterial complications (A, C, E, and G) and for a ferret infected with A/Sydney/5/97 (H3N2) which had both otitis media and sinusitis on imaging (B, D, F, H).