The etiology of respiratory diseases is complex. Influenza A and B viruses (family Orthomyxoviridae, genus Influenzavirus A and B) are frequently detected at all ages, but a variety of pathogens, including viruses and bacteria, cause similar symptoms that cannot be differentiated without laboratory confirmation. In Lao PDR, the influenza sentinel network was initiated only in 2007 3 and other respiratory viruses are normally not diagnosed. 3, 4 In particular, respiratory syncytial virus (RSV; order Mononegavirales, family Pneumoviridae, genus Orthopneumovirus, and species human orthopneumovirus) is a leading cause of lower respiratory tract infections in infants and young children worldwide. 5 A proper understanding of the etiology, seasonal patterns, and genetic diversity of respiratory viruses in Lao PDR is warranted. Notably, the success of the influenza vaccination recently introduced in the country relies on recommendations for optimal timing with respect to the season with highest influenza transmission. This is still poorly understood in subtropical countries. Nasopharyngeal swabs from patients with acute respiratory infections at the Luang Prabang Provincial Hospital in Northern Laos, catering to highland communities in Northern Laos, were screened for 13 viruses.
Samples were collected at the Provincial Hospital in Luang Prabang, a town with a population of 56 000 located at an altitude of 700 m. The hospital provides primary care without particular specialization to the local population of the town and is a major referral center for the highland communities living throughout this mountainous province. [9] [10] [11] human metapneumovirus (hMPV), 12 human coronaviruses 229E (hCoV-229E) and OC43 (hCoV-OC43). 13 The same pathogens as well as influenza B virus, human adenovirus (hAdV), human bocavirus (hBoV), human rhinovirus (hRV), and human coronavirus HKU1 (hCoV-HKU1) were detected by Lab2 using the FTD respiratory pathogens 21 kit (Fast-track Diagnostics, Esch-sur-Alzette, Luxembourg). All samples were tested by the two laboratories to compare detection rates of the in-house PCRs against commercial tests and to broaden the range of pathogens detected. Results of conventional PCRs were visualized on an agarose gel, and positivity was confirmed by sequencing on an ABI 3130 Avant Capillary Sequencer (Applied Biosystems, Nieuwerkerk, The Netherlands) using the PCR primers also as sequencing primers. The ectodomain of the G-gene of RSV was also amplified as described before 14 and sequenced (GenBank accession numbers MG773863-MG773881).
Genetic distances and phylogenetic trees were calculated using maximum composite likelihood model with 500 bootstrap values in MEGA6. 15 Figure 1A ). hAdV (40 of 309, 12.9%) and RSV (31 of 309, 10.0%) were also frequently detected, while the other viruses were detected in less than 10% of the patients, and PIV4 was not detected at all (Table 1) .
When comparing the results obtained by the two laboratories, more samples were positive for RSV and PIV1-3 in Lab1 compared to Lab2, while more samples were positive for influenza A, hMPV, hCoV-OC43, and hCoV-229E in Lab2 (Table 1) . Discrepant results were observed only in weak positive samples. A statistical difference between the results obtained by the two laboratories was only found for hCoV-OC43 (P = 0.041; Table 1 ), suggesting that most in-house PCRs were performing well and can be more sustainably used in resource-limited countries compared to commercial PCRs.
Dual and triple infections were detected in 12.9% (40 of 309) and
1.9% (6 of 309) of the patients (Table 1) 
All viruses combined, the virological status (ie, positivity for ≥1 virus) of the patients was not significantly associated with age. However, patients with viral mixed infections were significantly younger than those with a single infection (median age, 19.5 vs 28.0 months; P = 0.015). PIV2, PIV3, hMPV, hCoV-OC43, hCoV-229E, hAdV, and hBoV were also exclusively found in children under 15 years old (Table 1) , whereas influenza viruses were detected in all age groups and RSV (n = 1), PIV1 (n = 2), hCoV-HKU1 (n = 2), and hRV (n = 2) were only sporadically found in the 15-to 50-year age group (Table 1) 