Sunday, 10 April 2016

Colombia Zika virus report Week No. 13...

The latest epidemiological report, which includes data on Zika virus disease (ZVD; 27MAR2016-02APR2016), has been produced by the Colombian National Institute for Health team.[1]
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 a big week to 02-APR-2016 with the addition of 458 new laboratory confirmed ZIKV detections. 

It can't be known from these data, whether that is die to more testing, or a greater proportion of positives among those tested. There is not "total number of samples tested" denominator which can be used to gauge that. 


Excised from Colombian NIH PDF.[1]
I'm still not clear how the tally of confirmed cases is rising, but not showing up on the Colombian NIH graph (the red bars; the grey ones are clinical suspected cases). 

I've excised and posted the Colombian NIH graph to the left. 458 cases this week should show up clearly using that axis - it was the second biggest tally, just below Week No. 8 (also missing?) and 1.6X bigger than Week No. 4 which has been plotted and shows up clearly. I'm just assuming that the graph person has forgotten but would love to know if there is something else going on.

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 has been made to show the change in suspected cases. Most of these are not laboratory confirmed, but (I'm presuming here) include those that were from Graph No. 1.

These are people with rash, fever, joint pain etc that look to doctors as though they have disease that could be due to infection by ZIKV. This is not a reliable way of diagnosing a specific disease when other viral and non-viral agents are known to be co-circulating that can also cause rash, fever etc. But when resources are low or stretched thin, clicnial diagnosis is what there is. 

Interestingly, if you compare the patterns of green and red bar sizes - forgetting about actual values or missing data etc - the peak week for confirmed ZVD in Colombia, Week No. 8. was also the peak week for clinically suspected ZVD cases. 

There was also a rise in both measures in Week No. 13. Clinical suspicion is not laboratory confirmation, but there seem to be some overlapping trends there. 


In Guillain-Barre syndrome - it seems there has been a series of slightly decreasing diagnoses continuing in Week No. 13. Does that match up with the pattern of confirmed and suspected ZVD cases? Hard to tell but keep watching.
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). Data from [1]. 
Click on graph to enlarge.

Graph No. 3 shows that to Week No. 13, 10,261 suspected and 1,515 confirmed ZIKV infections have been identified in pregnant women. As of this report, 3 live births have been diagnosed with with microcephaly and were reported as being ZIKV positive; 30 other microcephaly diagnoses are under investigation. 
But, it isn't clear to me if these 3 are to be added to the 7 infections reported here, or if these 3 are 3 of the 7 - the other 4 being reported in the next epidemiological week.

Thanks as ever to Colombia's NIH for providing nice data around which we can all have a think and a chat about patterns.

References...

  1. http://www.ins.gov.co/boletin-epidemiologico/Boletn%20Epidemiolgico/2016%20Bolet%C3%ADn%20epidemiol%C3%B3gico%20semana%2013.pdf