Sunday 20 March 2016

Colombia updates the numbers..

The latest epidemiological report, which includes data on Zika virus disease (ZVD; week #10), has been produced by the excellent Colombian National Institute for Health team.[1] But people - 97 PDF pages long this week? You're making us all look bad!

Keep in mind that this, as with any report, only captures what it captures. Reports miss a lot of infections because a lot fo inectsion do not get tetsed or seen by a Doctor - espcially with a virus that reportedly only cuses symptoms in 1 of 5 people.

 Fast forwarding to Zika (Its a searchable PDF and "Zika" in Spanish translates into "Zika" in English) we find some interesting things.

Colombia reports 55,724 suspect, probable and confirmed ZVD cases since confirming the virus in epidemiological week 40, 2015.
  • 2,355 (4.2%) of those have been confirmed as positive via a laboratory test 
  • 46,556 (83.5%) have been "clinically confirmed" - which equates to a suspected case according to the World Health Organization (WHO) case definition I've copied out below. It is not clear to me from the Colombian report, whether any IgM testing has been conducted among these 46,556 - I am working under the assumption that it has not (please correct me if you have evidence otherwise)
  • 6,813 (12.2%) are reported as suspect cases

The downward trend in notifications I wrote about last week continues into the past week.

Reported Zika virus disease cases by epidemiological; week, 2015-2016.
The distributions were performed with n = 55,261 corresponding to the records
in the SIVIGILA notified. Image captured from [1] 
Since the beginning of the epidemic phase in Colombia, 10,319 ZVD cases have been reported in pregnant women

  • 995 (9.6%) of those have been confirmed as positive via a laboratory test (RT-PCR)
  • 8,229 (79.7%) have been "clinically confirmed" - which equates to a suspected case as discussed above
  • 1,095 (10.6%) are reported as suspected cases

Most of the "cases" in pregnant women have been notified during 2016's 10 epidemiological weeks, there have been 8,782 cases described in pregnant women (85.1% of the 10,319 total if I interpret the report correctly:
  • 845 (9.6%) of those in 2016 have been confirmed as  positive via a laboratory test (RT-PCR)
  • 6,997 (79.7%) in 2016 have been "clinically confirmed" - which equates to a suspected case as discussed above
  • 940 (10.7%) in 2016 are reported as suspected cases
The report notes 352 instances of neurological syndromes (248 are described as cases of Guillain-Barre syndrome) among mostly (57.1%) males. There is also a report of an increase in reports of acute flaccid paralysis in children under 15 years of age. 31 instances have been reported in children with a "documented" history of ZVD.
World Health Organization (WHO) interim definition for a case of ZVD [2; 12FEB2016]...

Suspected case
  • A person presenting with rash and/or fever and at least one of the following signs or symptoms:
    • arthralgia; or
    • arthritis; or
    • conjunctivitis (non-purulent/hyperaemic).
Probable case
  • A suspected case with presence of IgM antibody against Zika virus[a] and an epidemiological link[b]
Confirmed case

  • A person with laboratory confirmation of recent Zika virus infection:
    • presence of Zika virus RNA or antigen in serum or other samples (e.g. saliva, tissues, urine, whole blood); or
    • IgM antibody against Zika virus positive and PRNT90 for Zika virus with titre ≥20 and Zika virus PRNT90 titre ratio ≥ 4 compared to other flaviviruses; and exclusion of other flaviviruses
[a] With no evidence of infection with other flaviviruses
[b] Contact with a confirmed case, or a history of residing in or travelling to an area with local transmission of Zika virus within two weeks prior to onset of symptoms.

So while I adore the sheer amount of data in these reports from Colombia, there are - as is has ever been the case with Zika virus data in the Americas - some significant gaps. Here we see that most of the ZVD "cases" are suspect - not probable and certainly not confirmed. There is also no mention of brain malformations or microcephaly diagnoses among babies born to mothers with a confirmed history of ZVD - of which there have been a few. Perhaps they have not been confirmed yet?

We await more information from Colombian authorities on this issue because this is the next biggest outbreak of ZVD outside of Brazil and we expect to learn some things about the brain malformations and microcephaly diagnoses we have been hearing about from Brazil which may help us understand more of the role played by Zika virus. Or perhaps by other things that are Brazil-specific.
My thanks to Jorge Pontual for the early alert to the release of this reports-and the chats about it.

  2. WHO interim guideline for defining a ZVD case - 12FEB2016
  1. Noted that these figures are only based on people who present to a Doctor and will this miss many uinstances of ZIKV infection; stressed that the second part of the report was for pregnant women; highlighted that the Zika content is only part of the 97 page PDF - thanks DB

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