Sunday, 25 September 2016

Colombia Zika virus report, Epidemiological Week No. 37...

The latest epidemiological report from Colombia, which includes data on Zika virus disease (ZVD; 11SEP2016-17SEP2016), has been produced by the Colombian National Institute for Health team.[1]
NOTE: While these data were reported the past epidemiological week (EW), they may not be from that week. See earlier post about possible reporting lag.

As of this report, 41 (+1 from last EW) live births have been diagnosed with congenital ZIKV syndrome (CZVS; microcephaly/central nervous system disorder), confirmed as being ZIKV positive. That represents 0.70% of all confirmed ZIKV positive mothers-the 8th consecutive EW in which this proportion has risen.

Some back of napkin calculations looking at these numbers suggest that there are 7 deliveries for every 1,000 ZIKV-positive pregnant women that result in a ZIKV infected baby with microcephaly

This assumes each neonate has been tested for ZIKV as [2] suggests. This figure has no clear understanding of the number of aborted or miscarried foetuses that are also occurring from ZIKV-positive pregnant women. Abortions and miscarriages will need a local baseline to understand the scope of this component of the impact of ZIKV infection.

246 other microcephaly diagnoses (up from 216 last week) are now under investigation - this value had also been rising very quickly until a recent dip and plateau. Its rise once again might suggest suspicious CZVS cases in Colombia are accruing faster than the pace of complete investigation can keep up with. 

The graph below focuses on just the ZIKV-positive cases and those that remain under investigation, highlighting how the investigatory total has changed each week.

The change in confirmed ZIKV infection numbers when detected in
association with a microcephaly diagnosis, compared to the
preceding week's total (yellow bars, left-hand axis). Data are from [1].
Click on graph to enlarge.

It has now been 344 days, or 11 months 8 days, since ZIKV was first confirmed in Colombia on 16th October 2015.[2] Keep in mind that when talking about microcephaly - we have to think back in time to what insult or infection might have occurred during pregnancy. The counts of virus occurring this week will have zero impact on what happened back then. Also keep in mind that Colombia may be reporting things differently from Brazil.[3]

Brazil first reported positive (but unconfirmed) laboratory tests for Zika virus disease on 29th April 2015. Brazil then started to report a rise in foetal anomalies (an initial 141), in the form of microcephaly on 30th October 2015. This was 184 days - or about 6 months later.[4] However, the genetic analyses suggest Zika virus was in Brazil from around 2013. It had a lot longer to get established. Perhaps this is the difference between Brazil and Colombia.

But whatever the difference, there is a rise in microcephaly in Colombia compared to Brazil as we can see from the data in this Pan American Health Organization (PAHO) report...

401 cases counted up to EW 33 (now at EW 37) is 2.9X higher than the usual microcephaly figure per year for Colombia.
From PAHO report.[4]
References...

  1. http://www.ins.gov.co/boletin-epidemiologico/Boletn%20Epidemiolgico/2016%20Boletin%20epidemiologico%20semana%2037.pdf
  2. Zika Virus Disease in Colombia — Preliminary Report
    http://www.nejm.org/doi/full/10.1056/NEJMoa1604037#t=article
  3. http://virologydownunder.blogspot.com.au/2016/06/the-elephant-squeaked.html
  4. PAHO Zika-Epidemiological Report | Colombia
    http://www.paho.org/hq/index.php?option=com_docman&task=doc_view&gid=35139&Itemid=270&lang=en