Sunday, 17 July 2016

Colombia Zika virus report, Epidemiological Week No. 27...

The latest epidemiological report from Colombia, which includes data on Zika virus disease (ZVD; 03JUL2016-09JUL2016), has been produced by the Colombian National Institute for Health team.[1]
NOTE: While these data were reported the past epidemiological week, they may not be from that week. See earlier post about possible reporting lag.


Graph No.1. The cumulative curve of confirmed ZVD cases
(green circles, left-hand axis) and the change in confirmed ZVD case
numbers when compared to the preceding week's total
(green bars, right-hand axis). Data from [1].
Click on graph to enlarge.

Graph No. 1 shows that 176 new laboratory confirmed cases of ZVD were reported this week. The total sits at 8,826 or 10% (the highest proportion reported to date-steady for the  past 6 reporting weeks) of all clinically suspected Zika virus (ZIKV) detections.


Graph No.2. The cumulative curve of suspected ZVD cases
(pink circles, left-hand axis) and the change in suspected ZVD case
numbers when compared to the preceding week's total
(red bars, right-hand axis). Data from [1].
Click on graph to enlarge.
Graph No. 2 shows the change in suspected cases. These are not laboratory confirmed. The suspected ZVD cases continue to rise in a linear fashion, adding 984 this week to total 89,962.


Graph No.3. The cumulative curve of confirmed ZIKV infections
(lilac circles, left-hand axis) and the change in confirmed ZIKV infection
numbers when compared to the preceding week's total
(purple bars, right-hand axis). Now added the reported umber of microcephaly cases
confirmed as ZIKV infected (yellow bars, right-hand axis). To account for adjustments
that take cases away when there is no weekly case growth, a negative
value - the y-axes now allow for negative values. Data from [1].
Click on graph to enlarge.
Graph No. 3 shows that to epidemiological week (EW) No. 27, 11,614 suspected (+77 compared to last week) and 5,882 confirmed ZIKV infections (+135) have been identified in pregnant women.

As of this report, 21 (+3 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 0.36% of all confirmed ZIKV positive mothers-the 4th EW in which this proportion has risen.

Some back of napkin calculations looking at these numbers suggest that there are 3-4 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 [6] 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.

160  other microcephaly diagnoses (up from 112 last week and the highest value to date) are now under investigation - this value has also been rising very quickly and suggests suspicious CZVS cases in Colombia are accruing faster than the pace of complete investigation can keep up with. 

It now seems very likely that we can expect those bars to keep rising steeply in the coming weeks. The line is well and truly crossed.

Graph No. 4
below focuses on just the ZIKV-positive cases and those that remain under investigation, highlighting how the investigatory total has changed each week and been trending upwards since Epidemiological Week No. 14. 
Graph No.4. 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 275 days, or 9 months 1 day, since ZIKV was first confirmed in Colombia on 16th October 2015.[2] Colombia is currently carrying the next biggest load of ZVD cases, after Brazil.[3] Keep in mind that when talking about microcephaly - we have to think back in time to what insult or infection might have occurred in the first or second trimester (probably-still not definitive). 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.[5,7]

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]

References...