Since it first emerged in 2013, and until not quite 5 months ago, China had only reported LPAI (low pathogenic) versions of the H7N9 virus in both poultry and in humans.
While fully capable of causing severe, even fatal, illness in humans, the virus had always been benign in birds - including poultry.All of that changed on Feb 18th when China announced the discovery of two patients in Guangdong Province infected with a newly discovered highly pathogenic (HPAI) variant of H7N9 (see Guangdong CDC: Two H7N9 `Variants' Isolated From Human Cases). Additional HPAI samples were said to have been isolated in local poultry.
The following day, we also saw the Taiwan CDC announce that January's Imported H7N9 Case Carried the HPAI Mutation. All three cases showed signs of antiviral resistance, although it wasn't clear if that developed after they received treatment.
Since then, we've seen the rapid spread of HPAI H7N9 in poultry flocks (see map below), but have heard relatively little about additional human infections.
Although more cases were strongly suspected, it wasn't until about a month ago, in EID Journal: 2 Expedited HPAI H7N9 Studies, that we learned that 8 HPAI human infections had been identified from across three provinces (2 in Guangdong, 1 in Hunan, and 5 in Guangxi Province).
While still a small number, this indicated the the first 3 cases were not an isolated incident.Today we've a Rapid Communications from Eurosurveillance that increases the number of HPAI cases detected in Guangdong province from two to nine, and that compares the epidemiology, and course of illness, of these 9 HPAI cases to 51 LPAI H7N9 infections reported Guangdong this past winter.
Among their findings: sick or dead poultry from HPAI H7N9 may be a more efficient transmitter of the virus to humans than live, healthy LPAI H7N9 infected poultry.While average hospital stays for HPAI A(H7N9) patients were longer than for LPAI infected patients, outcomes and disease progression were comparable. Interestingly, only 2 of 9 HPAI human infections (22%) had underlying conditions, compared to 29 of 51 (57%) LPAI infections.
The small sample size of HPAI cases (n=9) makes it difficult to draw any firm conclusions on the relative severity of HPAI vs LPAI infection in humans, but those questions should be answered as more cases are analyzed.The full report has a lot more to offer, so follow the link below to read it in its entirety:
Eurosurveillance, Volume 22, Issue 27, 06 July 2017
Epidemiology of human infections with highly pathogenic avian influenza A(H7N9) virus in Guangdong, 2016 to 2017(SNIP)
M Kang 1 2 , EHY Lau 2 3 , W Guan 2 4 , Y Yang 1 , T Song 1 , BJ Cowling 3 , J Wu 1 , M Peiris 4 5 , J He 1 , CKP Mok 4 5
Correspondence: Jianfeng He (email@example.com)
Citation style for this article: Kang M, Lau EHY, Guan W, Yang Y, Song T, Cowling BJ, Wu J, Peiris M, He J, Mok CKP. Epidemiology of human infections with highly pathogenic avian influenza A(H7N9) virus in Guangdong, 2016 to 2017. Euro Surveill. 2017;22(27):pii=30568. DOI: http://dx.doi.org/10.2807/1560-7917.ES.2017.22.27.30568
Received:01 June 2017; Accepted:05 July 2017
We describe the epidemiology of highly pathogenic avian influenza (HPAI) A(H7N9) based on poultry market environmental surveillance and laboratory-confirmed human cases (n = 9) in Guangdong, China. We also compare the epidemiology between human cases of high- and low-pathogenic avian influenza A(H7N9) (n = 51) in Guangdong. Case fatality and severity were similar. Touching sick or dead poultry was the most important risk factor for HPAI A(H7N9) infections and should be highlighted for the control of future influenza A(H7N9) epidemics.
A novel avian influenza A(H7N9) virus emerged in mainland China in March 2013, and 1,533 human infections with 592 deaths have been reported to the World Health Organization as of June 2017 . The virus was low-pathogenic to poultry but caused varying disease severity in humans and there was an increase in virus detection in poultry and humans during winter [2-4]. There was a surge of human disease in the winter and spring period of 2016/17 with more than 500 reported cases of influenza A(H7N9) , surpassing the maximum number (ca 300 cases) of the previous four epidemic waves . The 2016/17 epidemic wave has extended to summer and not yet come to an end at the time of writing, much longer than the earlier epidemics.
Before the 2016/17 winter wave, all influenza A(H7N9) viruses identified from poultry and humans were low-pathogenic avian influenza (LPAI). However, influenza A(H7N9) viruses isolated from two human cases in Guangdong in mid-February 2017 showed insertion of four amino acids at the cleavage site of the haemagglutinin protein, indicating that the virus had become highly pathogenic to chickens [6,7]. In this study, we report the prevalence of the highly pathogenic avian influenza (HPAI) A(H7N9) virus in Guangdong poultry markets through active surveillance and compare the epidemiological characteristics and clinical outcomes between the patients infected with the HPAI and LPAI A(H7N9) viruses in Guangdong province during the 2016/17 season.
Clinical outcomes were comparable between hospitalised HPAI and LPAI A(H7N9) cases, except that the time from hospitalisation to discharge were longer for HPAI A(H7N9) cases. The importance of avoiding touching sick and dying poultry should be highlighted to the public for the control of HPAI A(H7N9).
Among those raising backyard poultry, 10 of 22 reported touching sick or dead poultry, while none reported touching sick or dead poultry among the 38 not raising backyard poultry. Strengthening awareness of the risks of backyard poultry will be crucial in the control of future HPAI A(H7N9) epidemics, especially since recent A(H7N9) cases have shifted to rural areas where backyard poultry is more prevalent .
We observed longer average hospital stays for HPAI A(H7N9) patients although there was no difference in clinical progression and outcome between HPAI and LPAI A(H7N9) patients. However, since there was no statistically significant difference in admission to ICU and clinical outcomes between HPAI and LPAI A(H7N9) patients, we still cannot determine whether the HPAI A(H7N9) viruses caused higher severity in patients.
That LPAI A(H7N9) patients had a shorter duration from hospitalisation to ICU admission and a smaller proportion with long duration from hospitalisation to death may be partially explained by the higher frequency of underlying conditions in this group. Detailed clinical investigation of virus shedding, virus dissemination and the levels of inflammation may be able to shed light on these questions.(Continue . . . )
Our analysis only focused on the comparison among severe influenza A(H7N9) patients. In earlier epidemics, a spectrum of cases from of asymptomatic to mild and severe was detected in Guangdong , however in the more recent epidemic waves in China, the detected cases tended to be more severe . Therefore, our understanding of the full range of severities of the HPAI A(H7N9) infections is still incomplete.