Paralysis was considered as a typical cardinal manifestation of stroke from the VA point of view since respondents can be expected to have a good recall of paralysis, especially when it is unilateral. Although paralysis alone may be an indication of conditions other than stroke, its presence in the VA questionnaire was taken as a certain indicator for stroke. The VA questionnaire used in Vietnam is designed to capture specific responses to structured questions as well as the narration of the respondents in the form of open ended free text. Hence, the response to paralysis was looked for in both these sections. As one can expect, there were more cases with positive response to the structured question (72%) than the mention of paralysis in the free text (52%) since a specific description of the symptom might have helped some respondents recall the condition of the patient who otherwise forgot to mention the symptom in their narration. Consistent with this expectation, there was good overlap of the mention of paralysis in the cases with a positive response to the structured question with two-thirds of respondents having given a positive response to structured question also mentioning paralysis in their narration. Hence, the structured question appears to be more sensitive in recording the symptom that is considered to be a typical clinical presentation of stroke.
On the other hand there were nine cases in which the respondents gave a negative response to the structured question but mentioned paralysis in their narration (out of a total of 73 cases with a negative response). There was also one case with mention of paralysis in the free text with a ‘don’t know’ response to the structured question (out of a total of 8 cases with a ‘don’t know’ response) and two instances with mention of paralysis in free text in cases where structured question responses were left blank by the interviewers. Although we have considered all these instances as a positive evidence of stroke in the VA in terms of presence of paralysis, it may be likely that the interpretation of ‘paralysis’ is different amongst respondents and interviewers depending on the prevalence of local dialects and fine shades of meaning. The interviewers, being paramedical personnel might have a more technical perspective of the term than respondents whose interpretation might be more general. For example, the term “liet” was used in the verbal autopsy questionnaire for “paralysis” but “liet” may also mean “transient limping” in some areas. Some respondents who actually denied the presence of paralysis mentioned “weakness” of the limbs or “inability to move” the limbs in their narration. From the clinical point of view, these cases cannot be considered as having paralysis as a symptom of stroke.
This difference in understanding meanings of the same word is also evident in the description of the term "stroke". With reference to stroke, there are two words in Vietnamese; viz. “dot quy” and “tai bien mach mau nao” that when translated into English mean stroke (or cerebrovascular condition). However, Vietnamese community perspectives on “dot quy” and “tai bien mach mau nao” seem to be different in many ways. The term “tai bien mach mau nao” has a more technical element and is generally used by the medical fraternity. This term resembles a clinical perception more than a community understanding of the condition. As a result, the positive responses to the structured question on history of stroke were more frequent in cases with hospital admission as this term was used for the particular question. In some cases, “tai bien mach mau nao” was mentioned in the free text by the respondents. However, all these cases had been in contact with health facilities in some way or the other.
The cases without an evidence of paralysis were examined for the presence of a history of stroke in the VA. Like paralysis, both structured question and free text were examined for the presence of a history of stroke. Respondents of 25 cases who responded ‘no’ to the history of stroke when specifically asked about it (structured question), mentioned about a history/diagnosis of stroke in their narration. This may again be due to differences in the understanding of interviewers and respondents. It is possible that the respondents might not have mentioned the exact word ‘stroke’ but the interviewers interpreted it by their explanation of the signs and symptoms of the disease (section 6.3). It may also seem apparent that a positive response to the past history of stroke is only likely from respondents of cases where the patient had a hospital admission. However, in contrast to this assumption, 71% of the cases in the nonhospital admission category also reported a past history of stroke (either in structured question or free text). This could be due to the fact that the cases without a hospital admission might have consulted a physician on an out-patient basis or have been in contact with a private health facility from where they became aware of the diagnosis of stroke.
With 90% of stroke cases diagnosed based on strong and medium-quality evidence, we can be confident that VA is a viable alternative to identify deaths caused by stroke in the current study. When a complete set of symptoms associated with stroke including paralysis, history of stroke, history of hypertension and unconsciousness was considered, one-third plus (37%) of the VA diagnosed stroke cases had this set of symptoms. However, it should be noted that history of hypertension is highly subject to recall by the respondents as is unconsciousness, although to a lesser extent. Also, there might have been some cases having both paralysis and unconsciousness but only unconsciousness was reported by the respondents in the VA as they might have been unable to recognize paralysis in presence of deep unconsciousness.
The differences in the responses to various symptoms in the cases by their status of hospital admission shows that the relatives of the deceased with hospital admission were better able to recall the symptoms. This finding is in accordance with the results of many previous studies that show the direct relation between patient access to health care facilities and the recall of symptoms by the relatives.[20
] This is an inherent source of bias and one of the major limitations in all validation studies that consider facility assigned diagnosis as the gold standard for comparison.
In addition to the limitations of VA described above, our study findings have potential limitations in terms of generalizability. As per the overall protocols, VA questionnaires were archived at each of the five medical universities that were charged with coordinating the mortality surveillance activity. Owing to time and resource constraints, we were able to confine our activities to only one medical university, and we chose to access and analyse the VA questionnaires from the four northern provinces for which activities were coordinated by Hanoi Medical University. Hence, our sample of 326 stroke deaths was only 22% of all stroke deaths in the national sample, which could limit the generalisabiity of our findings on quality of evidence in VA questionnaires. Further, we only explored the remaining 70 deaths assigned cardiovascular causes for potential misdiagnoses, in terms of presence of paralysis but classification to causes other than stroke. There is a likelihood of deaths assigned noncardiovascular causes also to have recorded paralysis but misdiagnosed to other causes. The overall surveillance protocol was based on physician review of VA questionnaires based on specific training programs in line with international standard guidelines for cause of death assignment from VA, adapted to the Vietnamese context. In case of diagnostic uncertainty, physician reviewers could assign a nonspecific cause, which accounted for 13.7% of all deaths in the overall data.[7
] We, therefore, anticipate that physician reviewers would have based their diagnoses according to the standard guidelines, and used the option of assigning a nonspecific cause where necessary. Despite this, there are likely to misclassification errors in the overall data, but we did not make an assessment of such errors, due to resource constraints. Given the magnitude of stroke mortality in the overall data, we chose to focus on the quality of evidence supporting stroke diagnosis from VA in a sample of cases for which stroke had been assigned as the underlying cause of death. To some extent, this possibly affects generalization of our findings on the quality of evidence to all stroke deaths in the overall study sample.