@article{StrengPrifertWeissbrichetal.2022,
  author    = {Streng, Andrea and Prifert, Christiane and Weissbrich, Benedikt and Sauerbrei, Andreas and Krumbholz, Andi and Schmid-Ott, Ruprecht and Liese, Johannes G.},
  title     = {Similar severity of influenza primary and re-infections in pre-school children requiring outpatient treatment due to febrile acute respiratory illness: prospective, multicentre surveillance study (2013-2015)},
  series = {BMC Infectious Diseases},
  volume    = {22},
  journal   = {BMC Infectious Diseases},
  doi       = {10.1186/s12879-021-06988-7},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-265841},
  year      = {2022},
  abstract  = {Background Influenza virus infections in immunologically na{\"i}ve children (primary infection) may be more severe than in children with re-infections who are already immunologically primed. We compared frequency and severity of influenza virus primary and re-infections in pre-school children requiring outpatient treatment. Methods Influenza-unvaccinated children 1-5 years of age presenting at pediatric practices with febrile acute respiratory infection < 48 h after symptom onset were enrolled in a prospective, cross-sectional, multicenter surveillance study (2013-2015). Influenza types/subtypes were PCR-confirmed from oropharyngeal swabs. Influenza type/subtype-specific IgG antibodies serving as surrogate markers for immunological priming were determined using ELISA/hemagglutination inhibition assays. The acute influenza disease was defined as primary infection/re-infection by the absence/presence of influenza type-specific immunoglobulin G (IgG) and, in a second approach, by the absence/presence of subtype-specific IgG. Socio-demographic and clinical data were also recorded. Results Of 217 influenza infections, 178 were due to influenza A (87 [49\%] primary infections, 91 [51\%] re-infections) and 39 were due to influenza B (38 [97\%] primary infections, one [3\%] re-infection). Children with "influenza A primary infections" showed fever with respiratory symptoms for a shorter period than children with "influenza A re-infections" (median 3 vs. 4 days; age-adjusted p = 0.03); other disease characteristics were similar. If primary infections and re-infections were defined based on influenza A subtypes, 122 (87\%) primary infections (78 "A(H3N2) primary infections", 44 "A(H1N1)pdm09 primary infections") and 18 (13\%) re-infections could be classified (14 "A(H3N2) re-infections" and 4 "A(H1N1)pdm09 re-infections"). Per subtype, primary infections and re-infections were of similar disease severity. Children with re-infections defined on the subtype level usually had non-protective IgG titers against the subtype of their acute infection (16 of 18; 89\%). Some patients infected by one of the influenza A subtypes showed protective IgG titers (≥ 1:40) against the other influenza A subtype (32/140; 23\%). Conclusions Pre-school children with acute influenza A primary infections and re-infections presented with similar frequency in pediatric practices. Contrary to expectation, severity of acute "influenza A primary infections" and "influenza A re-infections" were similar. Most "influenza A re-infections" defined on the type level turned out to be primary infections when defined based on the subtype. On the subtype level, re-infections were rare and of similar disease severity as primary infections of the same subtype. Subtype level re-infections were usually associated with low IgG levels for the specific subtype of the acute infection, suggesting only short-time humoral immunity induced by previous infection by this subtype. Overall, the results indicated recurring influenza virus infections in this age group and no or only limited heterosubtypic antibody-mediated cross-protection.},
  language  = {en}
}