Aetiology of influenza-like illness in adults includes parainfluenzavirus type 4

Abstract

Influenza viruses cause significant morbidity and mortality in adults each winter. At the same time, other respiratory viruses circulate and cause respiratory illness with influenza-like symptoms. Human respiratory syncytial virus (HRSV), human parainfluenza viruses (HPIV) and human metapneumovirus have all been associated with morbidity and mortality in adults, including nosocomial infections. This study evaluated 154 respiratory specimens collected from adults with influenza-like/acute respiratory illness (ILI) seen at the Edward Hines Jr VA Hospital, Hines, IL, USA, during two successive winters, 1998-1999 and 1999-2000. The samples were tested for ten viruses in two nested multiplex RT-PCRs. One to three respiratory viruses were detected in 68 % of the samples. As expected, influenza A virus (FLU-A) infections were most common (50 % of the samples), followed by HRSV-A (16 %). Surprisingly, HPIV-4 infections (5.8 %) were the third most prevalent. Mixed infections were also relatively common (11 %). When present, HPIV infections were approximately three times more likely to be included in a mixed infection than FLU-A or HRSV. Mixed infections and HPIV-4 are likely to be missed using rapid diagnostic tests. This study confirms that ILI in adults and the elderly can be caused by HRSV and HPIVs, including HPIV-4, which co-circulate with FLU-A.

Fig. 1.

Viruses identified during the 1998–1999 (a) and 1999–2000 (b) autumn/winter seasons. (a) During the 1998–1999 season, the peak of ILI occurred in weeks 4–6. FLU-A was the predominant virus identified in all 3 weeks. In weeks 4 and 5, all infections were caused by single viruses, but in week 6, multiple infections predominated: two FLU-A/HPIV-4A, one HRSV-A/HPIV-4A and one FLU-A/HRSV-A/HPIV-2. HPIV-4A appeared as the only detected virus in one patient during week 4, 8 days before HPIV-4A was found in three multiple infections in week 6. Additional multiple infections included: FLU-A/HPIV-4A (week 49) and FLU-A/HPIV-4B (week 3). (b) During the 1999–2000 winter season, the ILI peak occurred in weeks 52 to 2. FLU-A predominated in weeks 52 and 1, and HRSV-A in week 2. Multiple infections included: FLU-A/HRSV-A/HPIV-4A (week 48); FLU-A/HPIV-1 (week 50); FLU-A/HPIV-1 and two FLU-A/HPIV-2 (week 52); FLU-A/HPIV-4A, FLU-A/FLU-B/HRSV-A and FLU-A/HRSV-A (week 1); and three FLU-A/HRSV-A (week 2).