Despite having been identified in more than 700 patients since 2013 (and suspected to have infected many more), we've seen surprisingly few clusters of H7N9 reported by China's surveillance system.
That isn't to say there have been none.
We've seen a handful of household clusters over the years (see 2014 WHO H7N9 FAQ & EID Journal: H7N9 In Two Travelers Returning From China - Canada, 2015), and last November we looked at a report (see Study: Probable Nosocomial Transmission Of H7N9 In China) describing a small (n=2) cluster in a hospital ward in Zhejiang Province last February.
Today we've a short correspondence, appearing in the NEJM, describing a second nosocomial cluster that occurred in Shantou, Guandong province at roughly the same time.
In this case, two doctors attending a patient admitted with respiratory symptoms (later determined to be H7N9) were infected.
The index patient (M,28), who had frequent contact with poultry, was admitted to a Shantou hospital with respiratory symptoms on January 25th. Seven days later his attending physician (Pt #2, M,33) fell ill, followed 4 days later by a second attending physician in the same department (Pt #3, M,35).
All three were confirmed infected with H7N9 by RT-PCR, and while all recovered, the index patient was shown to be still shedding the virus 42 days after his initial onset of symptoms. Sequence and phylogenic analysis showed the three hospital isolates formed an independent clade that carried two unique nucleotide polymorphisms.
Follow the link below to read the full report and supplemental materials. I'll have a short comment when you return.
CorrespondenceN Engl J Med 2016; 374:596-598
February 11, 2016 DOI: 10.1056/NEJMc1505359
Although no sustained H7N9 transmission has been reported in the community (very few secondary infections detected in contacts of known cases) - since only the `sickest of the sick’ are ever tested - there’s a pretty good chance that a substantial number of mild cases go unnoticed.
One study conducted after the first wave in the spring of 2013 – where just 134 cases were recorded – estimated the real number of cases ran into the thousands (see Lancet: Clinical Severity Of Human H7N9 Infection).
The H7N9 virus continues to evolve and diversify over time (see EID Journal: H7N9’s Evolution During China’s Third Wave – Guangdong Province), and many researchers worry that it may eventually adapt well enough to human physiology to pose a genuine pandemic threat.
It may be entirely coincidental, but the day-to-day reporting of H7N9 out of China virtually stopped in early March of last year – at roughly the same time China was dealing with these two hospital clusters - something I blogged about in H7N9: No News Is . . . . Curious on March 19th.
Although the limited data we've seen suggests this year's outbreak may be lighter than the past two years, this report illustrates that is can sometimes take up to a year for some of the grittier details to filter out of China.